During August and September 2023,three giant icebergs,each bigger than Paris,successively grazed Clarence Island in the northeast of the Antarctic Peninsula,a home to a population of over 100000 penguins.This incident...During August and September 2023,three giant icebergs,each bigger than Paris,successively grazed Clarence Island in the northeast of the Antarctic Peninsula,a home to a population of over 100000 penguins.This incident may serve as a clarion call for the increasing iceberg calving due to global warming and its subsequent impact on the Antarctic ecosystem.Here we investigate this unexpected event and employ historical records and probabilistic analyses of iceberg grounding to assess the degree of impact on penguin colonies of Clarence Island.Among the eleven colonies,there is one with low impact,eight with medium impact,and two with high impact.The low-impact colony,Cape Lloyd,is located in the northern part of the island,while the high-impact colonies,False Ridge and Pink Pool,are in the southeast.The eight medium-impact colonies are distributed along both the eastern and western coasts of the island.This study provides essential support for evaluating the impact of iceberg activity on penguin colonies.We argue that penguin colonies located in areas prone to iceberg drift,such as Clarence Island,may become more vulnerable to the heightened risk of iceberg collisions or groundings in the warming future.Therefore,we hope the public will become more aware of the grave impacts of climate change on penguins and underscore the urgent need for effective conservation strategies.展开更多
In recent decades,Arctic summer sea ice extent(SIE)has shown a rapid decline overlaid with large interannual variations,both of which are influenced by geopotential height anomalies over Greenland(GL-high)and the cent...In recent decades,Arctic summer sea ice extent(SIE)has shown a rapid decline overlaid with large interannual variations,both of which are influenced by geopotential height anomalies over Greenland(GL-high)and the central Arctic(CA-high).In this study,SIE along coastal Siberia(Sib-SIE)and Alaska(Ala-SIE)is found to account for about 65%and 21%of the Arctic SIE interannual variability,respectively.Variability in Ala-SIE is related to the GL-high,whereas variability in Sib-SIE is related to the CA-high.A decreased Ala-SIE is associated with decreased cloud cover and increased easterly winds along the Alaskan coast,promoting ice-albedo feedback.A decreased Sib-SIE is associated with a significant increase in water vapor and downward longwave radiation(DLR)along the Siberian coast.The years 2012 and 2020 with minimum recorded ASIE are used as examples.Compared to climatology,summer 2012 is characterized by a significantly enhanced GL-high with major sea ice loss along the Alaskan coast,while summer 2020 is characterized by an enhanced CA-high with sea ice loss focused along the Siberian coast.In 2012,the lack of cloud cover along the Alaskan coast contributed to an increase in incoming solar radiation,amplifying ice-albedo feedback there;while in 2020,the opposite occurs with an increase in cloud cover along the Alaskan coast,resulting in a slight increase in sea ice there.Along the Siberian coast,increased DLR in 2020 plays a dominant role in sea ice loss,and increased cloud cover and water vapor both contribute to the increased DLR.展开更多
High-entropy diboride(HEB)ceramics constitute a novel class of ultrahigh-temperature ceramics that are appealing for applications in extreme environments.The relative density and grain size play important roles in tai...High-entropy diboride(HEB)ceramics constitute a novel class of ultrahigh-temperature ceramics that are appealing for applications in extreme environments.The relative density and grain size play important roles in tailoring the mechanical properties and wear resistance of HEBs,affecting their applications,such as high-temperature structural parts and thermal protection systems.In this study,highly dense(HfZrTaVNb)B_(2) ceramics with size-tunable microstructures were successfully synthesized by spark plasma sintering combined with an ingenious two-step strategy.The effects of grain size on the mechanical properties and wear resistance of(HfZrTaVNb)B_(2) ceramics were comprehensively investigated.The results indicated that the smaller grain size led to higher hardness and fracture toughness,and the relationship between hardness and grain size fitted the Hall–Petch equation well.In particular,the sample featuring a grain size of 1.64µm and 97.6%density had the highest hardness and fracture toughness,26.7 GPa and 4.6 MPa·m^(1/2),respectively.Notably,it also demonstrated optimal wear resistance,displaying a minimal wear rate of only 2.53×10^(−6) mm^(3)/(N·m)under a 20 N load.Microstructure analysis revealed that the primary wear mechanism observed in(HfZrTaVNb)B_(2) was oxidative wear under a 5 N load.Under a 10 N load,the wear mechanism comprised both oxidative and fracture wear.The wear mechanism became more complex and involved oxidation wear,fracture wear,abrasive wear,and fatigue wear at a 20 N load.展开更多
Herein,a novel kind of high-entropy MAX phases,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders were success-fully synthesized by a newly proposed two-step solid state reaction process.The oxidation experiments...Herein,a novel kind of high-entropy MAX phases,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders were success-fully synthesized by a newly proposed two-step solid state reaction process.The oxidation experiments demonstrate that the oxidation products of Al_(2)Mo_(3)O_(12) and rutile TiO 2 are formed at about 600 and 800℃,respectively.Besides,the dielectric and electromagnetic(EM)wave absorption properties of(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders and those after oxidation at different temperatures were also exam-ined.The results show that the as-synthesized(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders possess excellent EM wave absorption performances with the minimum reflection loss(RL)of-45.80 dB(at 1.7 mm thickness)and the maximum effective absorption bandwidth(E AB)of 3.6 GHz(at 1.5 mm thickness).After oxidation at 400-800℃,due to the coupling of conductivity loss and polarization loss,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders can retain good EM wave absorption properties in a certain frequency range.In this paper,the effects of oxidation on EM wave absorption properties of high-entropy MAX phases were systematically investigated for the first time.This work manifests that high-entropy MAX phases are promising EM wave absorbing candidates and can maintain good EM wave absorption performances after oxidation.展开更多
High-entropy MXenes,as a new emerging class of materials,possess diverse compositions,unexpected physicochemical characteristics,and great potentials for electromagnetic(EM)wave absorption.Herein,two single-to-few-lay...High-entropy MXenes,as a new emerging class of materials,possess diverse compositions,unexpected physicochemical characteristics,and great potentials for electromagnetic(EM)wave absorption.Herein,two single-to-few-layer high-entropy MXenes,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))3 C2 T_(x)and(Mo_(0.2)Cr_(0.2)Nb_(0.2)Ti_(0.2)V_(0.2))_(4)C_(3)T_(x),were synthesized for the first time.During the exfoliation and delamination processes,the structural,morphological,and compositional evolutions were analyzed,verifying the successful formation of single-to-few-layer two-dimensional MXene nanosheets.Investigations indicate that with the filling content of only 35 wt%,MXene powder filled composites exhibit high-efficiency EM wave absorption performances.The f-(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)C_(2)T_(x)possesses the minimum reflection loss(RL min)of−45.0 dB with the matching thickness of 1.52 mm and the maximum effective absorption bandwidth(EAB)of 5.6 GHz at 1.65 mm thickness.Also,f-(Mo_(0.2)Cr_(0.2)Nb_(0.2)Ti_(0.2)V_(0.2))_(4)C_(3)T_(x)can attain an RL min of−52.8 dB with the thickness of 1.58 mm and an optimum EAB value of 3.6 GHz at 1.50 mm.The satisfactory EM wave absorption efficiency and bandwidth,thin matching thickness,and low filling content prove the lightweight advantage and great application potential of high-entropy MXenes in EM wave absorption.In this work,the high-entropy strategy is applied to tune the EM wave absorption performances for MXenes.Furthermore,high-entropy engineering is expected to provide control and tunability of many other properties,such as electrochemical,catalytic,and mechanical behaviors.展开更多
Arctic sea ice plays an essential role in regional and global climate by dynamic processes and feedbacks associated with its high reflectivity, thermal insulation especially in presence of snow cover, and brine reject...Arctic sea ice plays an essential role in regional and global climate by dynamic processes and feedbacks associated with its high reflectivity, thermal insulation especially in presence of snow cover, and brine rejection [1]. Both observations and model simulations show that Arctic sea ice extent has dramatically declined and thinned in the past few decades [2] in response to global warming and cumulative anthropogenic greenhouse gas(GHG)emissions [3,4].展开更多
基金The National Natural Science Foundation of China under contract Nos 41925027 and 42206249.
文摘During August and September 2023,three giant icebergs,each bigger than Paris,successively grazed Clarence Island in the northeast of the Antarctic Peninsula,a home to a population of over 100000 penguins.This incident may serve as a clarion call for the increasing iceberg calving due to global warming and its subsequent impact on the Antarctic ecosystem.Here we investigate this unexpected event and employ historical records and probabilistic analyses of iceberg grounding to assess the degree of impact on penguin colonies of Clarence Island.Among the eleven colonies,there is one with low impact,eight with medium impact,and two with high impact.The low-impact colony,Cape Lloyd,is located in the northern part of the island,while the high-impact colonies,False Ridge and Pink Pool,are in the southeast.The eight medium-impact colonies are distributed along both the eastern and western coasts of the island.This study provides essential support for evaluating the impact of iceberg activity on penguin colonies.We argue that penguin colonies located in areas prone to iceberg drift,such as Clarence Island,may become more vulnerable to the heightened risk of iceberg collisions or groundings in the warming future.Therefore,we hope the public will become more aware of the grave impacts of climate change on penguins and underscore the urgent need for effective conservation strategies.
基金the National Key Research and Development Program of China(Grant Nos.2021YFC2802504 and 2019YFC1509104)the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant No.311021008).
文摘In recent decades,Arctic summer sea ice extent(SIE)has shown a rapid decline overlaid with large interannual variations,both of which are influenced by geopotential height anomalies over Greenland(GL-high)and the central Arctic(CA-high).In this study,SIE along coastal Siberia(Sib-SIE)and Alaska(Ala-SIE)is found to account for about 65%and 21%of the Arctic SIE interannual variability,respectively.Variability in Ala-SIE is related to the GL-high,whereas variability in Sib-SIE is related to the CA-high.A decreased Ala-SIE is associated with decreased cloud cover and increased easterly winds along the Alaskan coast,promoting ice-albedo feedback.A decreased Sib-SIE is associated with a significant increase in water vapor and downward longwave radiation(DLR)along the Siberian coast.The years 2012 and 2020 with minimum recorded ASIE are used as examples.Compared to climatology,summer 2012 is characterized by a significantly enhanced GL-high with major sea ice loss along the Alaskan coast,while summer 2020 is characterized by an enhanced CA-high with sea ice loss focused along the Siberian coast.In 2012,the lack of cloud cover along the Alaskan coast contributed to an increase in incoming solar radiation,amplifying ice-albedo feedback there;while in 2020,the opposite occurs with an increase in cloud cover along the Alaskan coast,resulting in a slight increase in sea ice there.Along the Siberian coast,increased DLR in 2020 plays a dominant role in sea ice loss,and increased cloud cover and water vapor both contribute to the increased DLR.
基金supported by the Key R&D Program of Shandong Province,China(2023CXGC010305).
文摘High-entropy diboride(HEB)ceramics constitute a novel class of ultrahigh-temperature ceramics that are appealing for applications in extreme environments.The relative density and grain size play important roles in tailoring the mechanical properties and wear resistance of HEBs,affecting their applications,such as high-temperature structural parts and thermal protection systems.In this study,highly dense(HfZrTaVNb)B_(2) ceramics with size-tunable microstructures were successfully synthesized by spark plasma sintering combined with an ingenious two-step strategy.The effects of grain size on the mechanical properties and wear resistance of(HfZrTaVNb)B_(2) ceramics were comprehensively investigated.The results indicated that the smaller grain size led to higher hardness and fracture toughness,and the relationship between hardness and grain size fitted the Hall–Petch equation well.In particular,the sample featuring a grain size of 1.64µm and 97.6%density had the highest hardness and fracture toughness,26.7 GPa and 4.6 MPa·m^(1/2),respectively.Notably,it also demonstrated optimal wear resistance,displaying a minimal wear rate of only 2.53×10^(−6) mm^(3)/(N·m)under a 20 N load.Microstructure analysis revealed that the primary wear mechanism observed in(HfZrTaVNb)B_(2) was oxidative wear under a 5 N load.Under a 10 N load,the wear mechanism comprised both oxidative and fracture wear.The wear mechanism became more complex and involved oxidation wear,fracture wear,abrasive wear,and fatigue wear at a 20 N load.
基金This work was financially supported by the Major Basic Re-search Projects of Shandong Natural Science Foundation(No.ZR2018ZB0104)the Science and Technology Development Project of Shandong Province(Nos.2016GGX102003,2017GGX20105)the Natural Science Foundation of Shandong Province(No.ZR2017BEM032).
文摘Herein,a novel kind of high-entropy MAX phases,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders were success-fully synthesized by a newly proposed two-step solid state reaction process.The oxidation experiments demonstrate that the oxidation products of Al_(2)Mo_(3)O_(12) and rutile TiO 2 are formed at about 600 and 800℃,respectively.Besides,the dielectric and electromagnetic(EM)wave absorption properties of(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders and those after oxidation at different temperatures were also exam-ined.The results show that the as-synthesized(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders possess excellent EM wave absorption performances with the minimum reflection loss(RL)of-45.80 dB(at 1.7 mm thickness)and the maximum effective absorption bandwidth(E AB)of 3.6 GHz(at 1.5 mm thickness).After oxidation at 400-800℃,due to the coupling of conductivity loss and polarization loss,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders can retain good EM wave absorption properties in a certain frequency range.In this paper,the effects of oxidation on EM wave absorption properties of high-entropy MAX phases were systematically investigated for the first time.This work manifests that high-entropy MAX phases are promising EM wave absorbing candidates and can maintain good EM wave absorption performances after oxidation.
基金supported by Major Basic Research Projects of Shandong Natural Science Foundation(ZR2018ZB0104)Science and Technology Development Project of Shandong Province(2016GGX102003,2017GGX20105)Natural Science Foundation of Shandong Province(ZR2017BEM032).
文摘High-entropy MXenes,as a new emerging class of materials,possess diverse compositions,unexpected physicochemical characteristics,and great potentials for electromagnetic(EM)wave absorption.Herein,two single-to-few-layer high-entropy MXenes,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))3 C2 T_(x)and(Mo_(0.2)Cr_(0.2)Nb_(0.2)Ti_(0.2)V_(0.2))_(4)C_(3)T_(x),were synthesized for the first time.During the exfoliation and delamination processes,the structural,morphological,and compositional evolutions were analyzed,verifying the successful formation of single-to-few-layer two-dimensional MXene nanosheets.Investigations indicate that with the filling content of only 35 wt%,MXene powder filled composites exhibit high-efficiency EM wave absorption performances.The f-(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)C_(2)T_(x)possesses the minimum reflection loss(RL min)of−45.0 dB with the matching thickness of 1.52 mm and the maximum effective absorption bandwidth(EAB)of 5.6 GHz at 1.65 mm thickness.Also,f-(Mo_(0.2)Cr_(0.2)Nb_(0.2)Ti_(0.2)V_(0.2))_(4)C_(3)T_(x)can attain an RL min of−52.8 dB with the thickness of 1.58 mm and an optimum EAB value of 3.6 GHz at 1.50 mm.The satisfactory EM wave absorption efficiency and bandwidth,thin matching thickness,and low filling content prove the lightweight advantage and great application potential of high-entropy MXenes in EM wave absorption.In this work,the high-entropy strategy is applied to tune the EM wave absorption performances for MXenes.Furthermore,high-entropy engineering is expected to provide control and tunability of many other properties,such as electrochemical,catalytic,and mechanical behaviors.
基金supported by the National Key Research and Development Program of China(2019YFC1509104)the National Natural Science Fundation of China for Distinguished Young Scholars(41925027)。
文摘Arctic sea ice plays an essential role in regional and global climate by dynamic processes and feedbacks associated with its high reflectivity, thermal insulation especially in presence of snow cover, and brine rejection [1]. Both observations and model simulations show that Arctic sea ice extent has dramatically declined and thinned in the past few decades [2] in response to global warming and cumulative anthropogenic greenhouse gas(GHG)emissions [3,4].
