Defense systems are needed to prevent catastrophic failures of a power grid due to cascaded events. Cascaded events can be attributed to improper operations of protective relays. The most challenging problem for the d...Defense systems are needed to prevent catastrophic failures of a power grid due to cascaded events. Cascaded events can be attributed to improper operations of protective relays. The most challenging problem for the design and implementation of a defense system is the performance in accuracy and speed in a real time environment. Protective devices are normally designed to operate fast in order to isolate the fault（s）. This paper proposes a new methodology to distinguish line overloads from actual faults for distance relays. In order to distinguish between line flow transfers from a line outage and an actual fault, the line outage distribution factor （LQDF） and generation shift factor （GSF） based power flow estimation method, and a secure peer to peer （P2P） communication structure are adopted. Computer simulations of cascaded events for a 6-bus system and the Korean power grid have been performed to establish the feasibility of the proposed scheme.展开更多
This paper is focused on the cascade refrigeration cycle using natural refrigerant CO 2-NH 3. The properties of refrigerants CO 2 and NH 3 are introduced and analyzed.CO 2 has the advantage in low stage of cascade ref...This paper is focused on the cascade refrigeration cycle using natural refrigerant CO 2-NH 3. The properties of refrigerants CO 2 and NH 3 are introduced and analyzed.CO 2 has the advantage in low stage of cascade refrigeration cycle due to its good characteristics and properties. The thermodynamic analysis results of the CO 2-NH 3 cascade refrigeration cycle demonstrates that the cycle has an optimum condensation temperature of low stage and also has an optimum flow rate ratio.By comparing with the R13-R22 and NH 3-NH 3 cascade refrigeration cycles, the mass flow rate ratio of CO 2-NH 3 is larger than those of R13-R22 and NH 3-NH 3, the theoretical COP of CO 2-NH 3 cascade refrigeration cycle is larger than that of the R13-R22 cascade cycle and smaller than that of the NH 3-NH 3 cascade cycle. But the real COP of CO 2-NH 3 cascade cycle will be higher than those of R13-R22 and NH 3-NH 3 because the specific volume of CO 2 at low temperature does not change much and its dynamic viscosity is also small.展开更多
Bridged polycyclic lactams are important structural units in organic functional materials,natural products,and pharmaceuticals.A flexible and efficient anion cascade reaction was developed for the preparation of bridg...Bridged polycyclic lactams are important structural units in organic functional materials,natural products,and pharmaceuticals.A flexible and efficient anion cascade reaction was developed for the preparation of bridged polycyclic lactams from readily available malonamides and 1,4‑dien-3-ones.Various highly substituted bridged polycyclic lactams were synthesized in good to excellent yields by tandem nucleophilic sequences in the presence of t BuOK in commercially available EtOH solvent at 60℃.Notably,the simple reactions can be run on a gram scale.Mechanistically,bis-Michael addition reaction and hemiaminalization reactions are involved in the tandem transformation.展开更多
A novel method for the preparation of highly functionalized 4-oxo-3-(1H-pyrrol-3-yl)-4H-chromenes(OPCMs)from 3-formylchromones andα-isocyanoacetates via an unprecedented three-component[1+1+3]cycloaddition reaction i...A novel method for the preparation of highly functionalized 4-oxo-3-(1H-pyrrol-3-yl)-4H-chromenes(OPCMs)from 3-formylchromones andα-isocyanoacetates via an unprecedented three-component[1+1+3]cycloaddition reaction in one pot was developed.The three-component cascade reaction was enabled by refluxing a mixture of the substrates in 1,4-dioxane in the presence of Ag_(2)CO_(3) as a Lewis acid promoter.As a result,a series of functionalized pyrroles(OPCMs,3),was prepared regioselectively and in high yields(80%-88%)through the formation of three bonds.This protocol can be used in the synthesis of OPCMs rather than through conventional,multi-step reactions and is suitable for both combinatorial and parallel syntheses of pyrroles.展开更多
以N,N-二甲基甲酰胺作溶剂,2-对甲苯乙炔基苯酚和α-环己烯酮在氯化钯和四丁基碘化铵的作用下,可以顺利发生分子内环化反应一步合成3-(2-对甲苯基苯并呋喃-3-基)环己-2-烯酮。反应最佳条件为:n(2-对甲苯乙炔基苯酚)∶n(α-环己烯酮)∶n...以N,N-二甲基甲酰胺作溶剂,2-对甲苯乙炔基苯酚和α-环己烯酮在氯化钯和四丁基碘化铵的作用下,可以顺利发生分子内环化反应一步合成3-(2-对甲苯基苯并呋喃-3-基)环己-2-烯酮。反应最佳条件为:n(2-对甲苯乙炔基苯酚)∶n(α-环己烯酮)∶n(氯化钯)∶n(四丁基碘化铵)=1∶5∶0.05∶1,反应温度为100℃,反应时间为24h,反应最佳产率82.0%。产物经1 H NMR、13 CNMR和GC-MS确征。展开更多
The rapid recombination of photo-generated electron-hole pairs,insufficient active sites,and strong photocorrosion have considerably restricted the practical application of Cd S in photocatalytic fields.Herein,we desi...The rapid recombination of photo-generated electron-hole pairs,insufficient active sites,and strong photocorrosion have considerably restricted the practical application of Cd S in photocatalytic fields.Herein,we designed and constructed a 2D/2D/2D layered heterojunction photocatalyst with cascaded 2D coupling interfaces.Experiments using electron spin resonance spectroscopy,ultraviolet photoelectron spectroscopy,and in-situ irradiation X-ray photoelectron spectroscopy were conducted to confirm the 2D layered CdS/WO_(3) step-scheme(S-scheme)heterojunctions and CdS/MX ohmic junctions.Impressively,it was found that the strong interfacial electric fields in the S-scheme heterojunction photocatalysts could effectively promote spatially directional charge separation and transport between CdS and WO_(3) nanosheets.In addition,2D Ti_(3)C_(2) MXene nanosheets with a smaller work function and excellent metal conductivity when used as a co-catalyst could build ohmic junctions with Cd S nanosheets,thus providing a greater number of electron transfer pathways and hydrogen evolution sites.Results showed that the highest visible-light hydrogen evolution rate of the optimized MX-Cd S/WO_(3) layered multi-heterostructures could reach as high as 27.5 mmol/g/h,which was 11.0 times higher than that of pure CdS nanosheets.Notably,the apparent quantum efficiency reached 12.0% at 450 nm.It is hoped that this study offers a reliable approach for developing multifunctional photocatalysts by integrating S-scheme and ohmic-junction built-in electric fields and rationally designing a 2D/2D interface for efficient light-to-hydrogen fuel production.展开更多
基金Ministry of Science&Technology of Korea and Korea Science&Engineering Foundation Through ERC(Engineering Research Center)Program.
文摘Defense systems are needed to prevent catastrophic failures of a power grid due to cascaded events. Cascaded events can be attributed to improper operations of protective relays. The most challenging problem for the design and implementation of a defense system is the performance in accuracy and speed in a real time environment. Protective devices are normally designed to operate fast in order to isolate the fault（s）. This paper proposes a new methodology to distinguish line overloads from actual faults for distance relays. In order to distinguish between line flow transfers from a line outage and an actual fault, the line outage distribution factor （LQDF） and generation shift factor （GSF） based power flow estimation method, and a secure peer to peer （P2P） communication structure are adopted. Computer simulations of cascaded events for a 6-bus system and the Korean power grid have been performed to establish the feasibility of the proposed scheme.
文摘This paper is focused on the cascade refrigeration cycle using natural refrigerant CO 2-NH 3. The properties of refrigerants CO 2 and NH 3 are introduced and analyzed.CO 2 has the advantage in low stage of cascade refrigeration cycle due to its good characteristics and properties. The thermodynamic analysis results of the CO 2-NH 3 cascade refrigeration cycle demonstrates that the cycle has an optimum condensation temperature of low stage and also has an optimum flow rate ratio.By comparing with the R13-R22 and NH 3-NH 3 cascade refrigeration cycles, the mass flow rate ratio of CO 2-NH 3 is larger than those of R13-R22 and NH 3-NH 3, the theoretical COP of CO 2-NH 3 cascade refrigeration cycle is larger than that of the R13-R22 cascade cycle and smaller than that of the NH 3-NH 3 cascade cycle. But the real COP of CO 2-NH 3 cascade cycle will be higher than those of R13-R22 and NH 3-NH 3 because the specific volume of CO 2 at low temperature does not change much and its dynamic viscosity is also small.
基金National Natural Science Foundation of China(NSFC,Nos.21772032,21877206,and 22101074)the 111 Project(No.D17007)+3 种基金Excellent Youth Foundation of Henan Scientific Committee(No.222300420012)China Postdoctoral Science Foundation(No.2019M660173)the Natural Science Foundation of Henan Province(No.202300410233)Henan Key Laboratory of Organic Functional Molecules and Drug Innovation for financial support。
文摘Bridged polycyclic lactams are important structural units in organic functional materials,natural products,and pharmaceuticals.A flexible and efficient anion cascade reaction was developed for the preparation of bridged polycyclic lactams from readily available malonamides and 1,4‑dien-3-ones.Various highly substituted bridged polycyclic lactams were synthesized in good to excellent yields by tandem nucleophilic sequences in the presence of t BuOK in commercially available EtOH solvent at 60℃.Notably,the simple reactions can be run on a gram scale.Mechanistically,bis-Michael addition reaction and hemiaminalization reactions are involved in the tandem transformation.
基金the Natural Science Foundation of Yunnan Province(No.2019FY003003)the National Natural Science Foundation of China(No.21662042)the Scientific and Technological Innovation Team of Green Synthesis and Activity Research of Natural-like Heterocyclic Compound Libraries in Universities of Yunnan Province(No.C17624011121).
文摘A novel method for the preparation of highly functionalized 4-oxo-3-(1H-pyrrol-3-yl)-4H-chromenes(OPCMs)from 3-formylchromones andα-isocyanoacetates via an unprecedented three-component[1+1+3]cycloaddition reaction in one pot was developed.The three-component cascade reaction was enabled by refluxing a mixture of the substrates in 1,4-dioxane in the presence of Ag_(2)CO_(3) as a Lewis acid promoter.As a result,a series of functionalized pyrroles(OPCMs,3),was prepared regioselectively and in high yields(80%-88%)through the formation of three bonds.This protocol can be used in the synthesis of OPCMs rather than through conventional,multi-step reactions and is suitable for both combinatorial and parallel syntheses of pyrroles.
文摘以N,N-二甲基甲酰胺作溶剂,2-对甲苯乙炔基苯酚和α-环己烯酮在氯化钯和四丁基碘化铵的作用下,可以顺利发生分子内环化反应一步合成3-(2-对甲苯基苯并呋喃-3-基)环己-2-烯酮。反应最佳条件为:n(2-对甲苯乙炔基苯酚)∶n(α-环己烯酮)∶n(氯化钯)∶n(四丁基碘化铵)=1∶5∶0.05∶1,反应温度为100℃,反应时间为24h,反应最佳产率82.0%。产物经1 H NMR、13 CNMR和GC-MS确征。
文摘The rapid recombination of photo-generated electron-hole pairs,insufficient active sites,and strong photocorrosion have considerably restricted the practical application of Cd S in photocatalytic fields.Herein,we designed and constructed a 2D/2D/2D layered heterojunction photocatalyst with cascaded 2D coupling interfaces.Experiments using electron spin resonance spectroscopy,ultraviolet photoelectron spectroscopy,and in-situ irradiation X-ray photoelectron spectroscopy were conducted to confirm the 2D layered CdS/WO_(3) step-scheme(S-scheme)heterojunctions and CdS/MX ohmic junctions.Impressively,it was found that the strong interfacial electric fields in the S-scheme heterojunction photocatalysts could effectively promote spatially directional charge separation and transport between CdS and WO_(3) nanosheets.In addition,2D Ti_(3)C_(2) MXene nanosheets with a smaller work function and excellent metal conductivity when used as a co-catalyst could build ohmic junctions with Cd S nanosheets,thus providing a greater number of electron transfer pathways and hydrogen evolution sites.Results showed that the highest visible-light hydrogen evolution rate of the optimized MX-Cd S/WO_(3) layered multi-heterostructures could reach as high as 27.5 mmol/g/h,which was 11.0 times higher than that of pure CdS nanosheets.Notably,the apparent quantum efficiency reached 12.0% at 450 nm.It is hoped that this study offers a reliable approach for developing multifunctional photocatalysts by integrating S-scheme and ohmic-junction built-in electric fields and rationally designing a 2D/2D interface for efficient light-to-hydrogen fuel production.
