High-entropy alloys(HEAs)have attracted extensive attention ascribed to their unique physical and chemical properties induced by the cocktail effect.However,their oxidation behaviors,in particular at nanoscale,are sti...High-entropy alloys(HEAs)have attracted extensive attention ascribed to their unique physical and chemical properties induced by the cocktail effect.However,their oxidation behaviors,in particular at nanoscale,are still lack because of multi-element complexity,which could also be completely differ-ent from the bulk counterparts.In this work,we synthesized FeCoNiTiCu five-element HEA nanopar-ticles(NPs)with uniform elemental distribution by arc-discharging approach,and further investigated their oxidation behaviors at 250 ℃,and 350 ℃.The morphology,structure and element distribution of NPs were analyzed by transmission electron microscopy(TEM),energy dispersive spectroscopy(EDS)and electron energy loss spectroscopy(EELS).The surface oxidation in FeCoNiTiCu NPs during the high-temperature process can induce nanoscale pores at core/shell interfaces by Kirkendall effect,and even the eventual coalescence into a single cavity.Additionally,the oxidation states of NPs with diameters(d)varying from 60 to 350 nm were analyzed in detail,revealing two typical configurations:hollow(d<150 nm)and yolk-shell structures(d>150 nm).The experimental results were complemented by first-principles calculations to investigate the diffusion behaviors of five elements,evidencing that the surface oxidation strongly alters the surface segregation preferences:(1)in the initial stage,Cu and Ni appear to prefer segregating on the surface,while Co,Ti and Fe tend to stay in the bulk;(2)in the oxidation process,Cu prefers to stay in the center,while Ti segregates to the surface ascribed to the reduced po-tential energies.The study gives new insights into oxidation of nanoscale HEA,and also provides a way for fabrication of high-entropy oxides with controllable architectures.展开更多
For deep geological disposal of high-level radioactive waste(HLW)in granite,the temperature on the HLW canisters is commonly designed to be lower than100fiC.This criterion dictates the dimension of the repository.Base...For deep geological disposal of high-level radioactive waste(HLW)in granite,the temperature on the HLW canisters is commonly designed to be lower than100fiC.This criterion dictates the dimension of the repository.Based on the concept of HLW disposal in vertical boreholes,thermal process in the nearfield(host rock and buffer)surrounding HLW canisters has been simulated by using different methods.The results are drawn as follows:(a)the initial heat power of HLW canisters is the most important and sensitive parameter for evolution of temperaturefield;(b)the thermal properties and variations of the host rock,the engineered buffer,and possible gaps between canister and buffer and host rock are the additional key factors governing the heat transformation;(c)the gaps width and thefilling by water or air determine the temperature offsets between them.展开更多
Concurrency is a common feature in most industrial systems,where several components can execute different actions simultaneously.In this paper,we first introduce a new feasible nonblocking concurrent supervisory contr...Concurrency is a common feature in most industrial systems,where several components can execute different actions simultaneously.In this paper,we first introduce a new feasible nonblocking concurrent supervisory control map for a concurrent system,and subsequently,new concepts of concurrent controllability and concurrent observability.Then we present a sufficient and necessary condition for the existence of a feasible nonblocking concurrent supervisory controlmap to achieve a given concurrent language.After introducing a new concept of prefix-closed concurrent normality,we show that the supremal concurrently controllable and prefix-closed concurrently normal sublanguages exist and are computable.Our emphasis here is not to address the computational efficiency of solving concurrent supervisory control problems,which is still a technical challenge,but to show that the commonly used Ramadge–Wonham asynchronous control is simply a special case of our proposed concurrent control framework by providing an insightful treatment on compound events.展开更多
基金National Science Fund for Distinguished Young Scholars(No.52225312)Key Research and Development Program of Zhejiang Province(Nos.2021C01033,2023C01077)National Natural Science Foundation of China(No.U1908220).
文摘High-entropy alloys(HEAs)have attracted extensive attention ascribed to their unique physical and chemical properties induced by the cocktail effect.However,their oxidation behaviors,in particular at nanoscale,are still lack because of multi-element complexity,which could also be completely differ-ent from the bulk counterparts.In this work,we synthesized FeCoNiTiCu five-element HEA nanopar-ticles(NPs)with uniform elemental distribution by arc-discharging approach,and further investigated their oxidation behaviors at 250 ℃,and 350 ℃.The morphology,structure and element distribution of NPs were analyzed by transmission electron microscopy(TEM),energy dispersive spectroscopy(EDS)and electron energy loss spectroscopy(EELS).The surface oxidation in FeCoNiTiCu NPs during the high-temperature process can induce nanoscale pores at core/shell interfaces by Kirkendall effect,and even the eventual coalescence into a single cavity.Additionally,the oxidation states of NPs with diameters(d)varying from 60 to 350 nm were analyzed in detail,revealing two typical configurations:hollow(d<150 nm)and yolk-shell structures(d>150 nm).The experimental results were complemented by first-principles calculations to investigate the diffusion behaviors of five elements,evidencing that the surface oxidation strongly alters the surface segregation preferences:(1)in the initial stage,Cu and Ni appear to prefer segregating on the surface,while Co,Ti and Fe tend to stay in the bulk;(2)in the oxidation process,Cu prefers to stay in the center,while Ti segregates to the surface ascribed to the reduced po-tential energies.The study gives new insights into oxidation of nanoscale HEA,and also provides a way for fabrication of high-entropy oxides with controllable architectures.
文摘For deep geological disposal of high-level radioactive waste(HLW)in granite,the temperature on the HLW canisters is commonly designed to be lower than100fiC.This criterion dictates the dimension of the repository.Based on the concept of HLW disposal in vertical boreholes,thermal process in the nearfield(host rock and buffer)surrounding HLW canisters has been simulated by using different methods.The results are drawn as follows:(a)the initial heat power of HLW canisters is the most important and sensitive parameter for evolution of temperaturefield;(b)the thermal properties and variations of the host rock,the engineered buffer,and possible gaps between canister and buffer and host rock are the additional key factors governing the heat transformation;(c)the gaps width and thefilling by water or air determine the temperature offsets between them.
基金The support from Singapore Ministry of Education Tier 1 Academic Research[grant number M4011221.040 RG84/13]is gratefully acknowledged.
文摘Concurrency is a common feature in most industrial systems,where several components can execute different actions simultaneously.In this paper,we first introduce a new feasible nonblocking concurrent supervisory control map for a concurrent system,and subsequently,new concepts of concurrent controllability and concurrent observability.Then we present a sufficient and necessary condition for the existence of a feasible nonblocking concurrent supervisory controlmap to achieve a given concurrent language.After introducing a new concept of prefix-closed concurrent normality,we show that the supremal concurrently controllable and prefix-closed concurrently normal sublanguages exist and are computable.Our emphasis here is not to address the computational efficiency of solving concurrent supervisory control problems,which is still a technical challenge,but to show that the commonly used Ramadge–Wonham asynchronous control is simply a special case of our proposed concurrent control framework by providing an insightful treatment on compound events.
