Large eddy simulation （LES） is used to investigate contrasting dynamic characteristics of shear turbulence （ST） and Langmuir circulation （LC） in the surface mixed layer （SML）. ST is usually induced by wind for...Large eddy simulation （LES） is used to investigate contrasting dynamic characteristics of shear turbulence （ST） and Langmuir circulation （LC） in the surface mixed layer （SML）. ST is usually induced by wind forcing in SML. LC can be driven by wave-current interaction that includes the roles of wind, wave and vortex forcing. The LES results show that LC suppresses the horizontal velocity and greatly modifies the downwind velocity profile, but increases the vertical velocity. The strong downweUing jets of LC accelerate and increase the downward transport of energy as compared to ST. The vertical eddy viscosity Km of LC is much larger than that of ST. Strong mixing induced by LC has two locations. They are located in the 26s-36s （Stokes depth scale） and the lower layer of the SML, respectively. Its value and position change periodically with time. In contrast, maximum Km induced by ST is located in the middle depth of the SML. The turbulent kinetic energy （TKE） generated by LC is larger than that by ST. The differences in vertical distributions of TKE and Krn are evident. Therefore, the parameterization of LC cannot be solely based on TKE. For deep SML, the convection of large-scale eddies in LC plays a main role in downward transport of energy and LC can induce stronger velocity shear （S2） near the SML base. In addition, the large-scale eddies and Sz induced by LC is changing all the time, which needs to be fully considered in the parameterization of LC.展开更多
Using surface and aerological meteorological observations obtained at the Xisha Automatic Weather Station and three moored buoys along the continental slope, characteristics of the synoptic-scale disturbances over the...Using surface and aerological meteorological observations obtained at the Xisha Automatic Weather Station and three moored buoys along the continental slope, characteristics of the synoptic-scale disturbances over the northern South China Sea （NSCS） are extensively studied. The power spectra of surface and aerological observations suggest a synoptic feature with a pronounced energy peak at a period of 5–8 d and a weak peak at 3–4 d. The standard deviation of the synoptic temperature component derived at Xisha Station from 1976 to 2011 indicates that the strongest variability normally exists in August all through the whole troposphere. At the interannual scale, it is found that El Nin o plays an important role in regulating the synoptic disturbances of atmosphere. The vertical synoptic disturbances have a double active peak following El Nin o condition. The first peak usually occurs during the mature phase of El Nin o, and the second one occurs in the summer of decay year. Comparing with the summer of developing years, the summer of the decaying year of El Nin o has more active and stronger synoptic disturbances, especially for the 5–8 d period variations.展开更多
Recent progress of physical oceanography in the South China Sea (SCS) associated with the western boundary current (WBC) and eddies is reviewed in this paper. It includes Argo observations of the WBC, eddy detection i...Recent progress of physical oceanography in the South China Sea (SCS) associated with the western boundary current (WBC) and eddies is reviewed in this paper. It includes Argo observations of the WBC, eddy detection in the WBC based on satellite images, cross-continental shelf exchange in the WBC, eddy-current interaction, interannual variability of the WBC, air-sea interaction, the SCS throughflow (SCSTF), among others. The WBC in the SCS is strong, and its structure, variability and dynamic processes on seasonal and interannual time scales are yet to be fully understood. In this paper, we summarize progresses on the variability of the WBC, eddy-current interaction, air-sea interaction, and the SCSTF achieved in the past few years. Firstly, using the drifting buoy observations, we point out that the WBC becomes stronger and narrower after it reaches the central Vietnam coast. The possible mechanisms influencing the ocean circulation in the northern SCS are discussed, and the dynamic mechanisms that induce the countercurrent in the region of northern branch of WBC in winter are also studied quantitatively using momentum balance. The geostropic component of the WBC was diagnosed using the ship observation along 18°N, and we found that the WBC changed significantly on interannual time scale. Secondly, using the ship observations, two anti-cyclonic eddies in the winter of 2003/2004 in the northern SCS, and three anti-cyclonic eddies in the summer of 2007 along 18°N were studied. The results show that the two anti-cyclonic eddies can propagate southwestward along the continental shelf at the speed of first Rossby wave (～0.1 ms-1 ) in winter, and the interaction between the three anti-cyclonic eddies in summer and the WBC in the SCS is preliminarily revealed. Eddies on the continental shelf of northern SCS propagated southeastward with a maximum speed of 0.09 ms-1 , and those to the east of Vietnam coast had the largest kinetic energy, both of which imply strong interaction between eddy activity and WBC in the SCS. Thirdly, strong intraseasonal variability (ISV) of sea surface temperature (SST) near the WBC regions was found, and the ISV signal of SST in winter weakens the ISV signal of latent heat flux by 20%. Fourthly, the long-term change of SCSTF volume transport and its connection with the ocean circulation in the Pacific were discussed.展开更多
Metal-organic frameworks(MOFs)composed of functional metal ions/clusters and suitable bridging ligands are highly designable,which have shown excellent catalytic activity as nanozymes and are promising for antibacteri...Metal-organic frameworks(MOFs)composed of functional metal ions/clusters and suitable bridging ligands are highly designable,which have shown excellent catalytic activity as nanozymes and are promising for antibacterial therapy.Herein,twodimensional(2D)copper MOF nanosheets(Cu-MOF NSs)as effective antibacterial agents were prepared through a simple onestep method.The 2D Cu-MOF NSs displayed a peroxidase-like activity toward H_(2)O_(2)decomposition into highly cytotoxic hydroxyl radicals(·OH).Notably,the 2D morphology of Cu-MOF NSs provides a high density of Cu^(2+)/Cu^(+)surface active sites,which could efficiently oxidize the proteins and lipids on the bacterial surface and induce the death of bacteria.It is found that the as-prepared 2D Cu-MOF NSs exhibited antibacterial properties against Staphylococcus aureus(S.aureus)and could efficiently eradicate the biofilm of S.aureus.Up to 99.9%bacteria were killed at a Cu-MOF concentration of 4μg/m L.This study opens a new avenue for the design of MOF-based antibacterial agents to combat pathogenic bacterial infections.展开更多
基金The National Basic Research Program of China(973 Program)under contract No.2011CB403504the China Postdoctoral Science Foundation under contract No.2013M542216the National Natural Science Foundation of China under contract No.41206011
文摘Large eddy simulation （LES） is used to investigate contrasting dynamic characteristics of shear turbulence （ST） and Langmuir circulation （LC） in the surface mixed layer （SML）. ST is usually induced by wind forcing in SML. LC can be driven by wave-current interaction that includes the roles of wind, wave and vortex forcing. The LES results show that LC suppresses the horizontal velocity and greatly modifies the downwind velocity profile, but increases the vertical velocity. The strong downweUing jets of LC accelerate and increase the downward transport of energy as compared to ST. The vertical eddy viscosity Km of LC is much larger than that of ST. Strong mixing induced by LC has two locations. They are located in the 26s-36s （Stokes depth scale） and the lower layer of the SML, respectively. Its value and position change periodically with time. In contrast, maximum Km induced by ST is located in the middle depth of the SML. The turbulent kinetic energy （TKE） generated by LC is larger than that by ST. The differences in vertical distributions of TKE and Krn are evident. Therefore, the parameterization of LC cannot be solely based on TKE. For deep SML, the convection of large-scale eddies in LC plays a main role in downward transport of energy and LC can induce stronger velocity shear （S2） near the SML base. In addition, the large-scale eddies and Sz induced by LC is changing all the time, which needs to be fully considered in the parameterization of LC.
基金The aerological data of Xisha Station were downloaded from http://weather.uwyo.edu/upperair/sounding.html.by The National Natural Basic Research Program ("973" Program) of China, under contract No. 2011CB403501the Knowledge Innovation Project for Distinguished Young Scholar of the Chinese Academy of Sciences of China under contract No. KZCX2-EW-QN203+1 种基金the Knowledge Innovation Program of the Chinese Academy of Sciences of China under contract No. SQ200916the National Natural Science Foundation of China under contract Nos 41206011 and 41106028
文摘Using surface and aerological meteorological observations obtained at the Xisha Automatic Weather Station and three moored buoys along the continental slope, characteristics of the synoptic-scale disturbances over the northern South China Sea （NSCS） are extensively studied. The power spectra of surface and aerological observations suggest a synoptic feature with a pronounced energy peak at a period of 5–8 d and a weak peak at 3–4 d. The standard deviation of the synoptic temperature component derived at Xisha Station from 1976 to 2011 indicates that the strongest variability normally exists in August all through the whole troposphere. At the interannual scale, it is found that El Nin o plays an important role in regulating the synoptic disturbances of atmosphere. The vertical synoptic disturbances have a double active peak following El Nin o condition. The first peak usually occurs during the mature phase of El Nin o, and the second one occurs in the summer of decay year. Comparing with the summer of developing years, the summer of the decaying year of El Nin o has more active and stronger synoptic disturbances, especially for the 5–8 d period variations.
基金supported by the National Basic Research Program of China(2011CB403504)the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-EW-Y040)the National Natural Science Foundation of China (40830851)
文摘Recent progress of physical oceanography in the South China Sea (SCS) associated with the western boundary current (WBC) and eddies is reviewed in this paper. It includes Argo observations of the WBC, eddy detection in the WBC based on satellite images, cross-continental shelf exchange in the WBC, eddy-current interaction, interannual variability of the WBC, air-sea interaction, the SCS throughflow (SCSTF), among others. The WBC in the SCS is strong, and its structure, variability and dynamic processes on seasonal and interannual time scales are yet to be fully understood. In this paper, we summarize progresses on the variability of the WBC, eddy-current interaction, air-sea interaction, and the SCSTF achieved in the past few years. Firstly, using the drifting buoy observations, we point out that the WBC becomes stronger and narrower after it reaches the central Vietnam coast. The possible mechanisms influencing the ocean circulation in the northern SCS are discussed, and the dynamic mechanisms that induce the countercurrent in the region of northern branch of WBC in winter are also studied quantitatively using momentum balance. The geostropic component of the WBC was diagnosed using the ship observation along 18°N, and we found that the WBC changed significantly on interannual time scale. Secondly, using the ship observations, two anti-cyclonic eddies in the winter of 2003/2004 in the northern SCS, and three anti-cyclonic eddies in the summer of 2007 along 18°N were studied. The results show that the two anti-cyclonic eddies can propagate southwestward along the continental shelf at the speed of first Rossby wave (～0.1 ms-1 ) in winter, and the interaction between the three anti-cyclonic eddies in summer and the WBC in the SCS is preliminarily revealed. Eddies on the continental shelf of northern SCS propagated southeastward with a maximum speed of 0.09 ms-1 , and those to the east of Vietnam coast had the largest kinetic energy, both of which imply strong interaction between eddy activity and WBC in the SCS. Thirdly, strong intraseasonal variability (ISV) of sea surface temperature (SST) near the WBC regions was found, and the ISV signal of SST in winter weakens the ISV signal of latent heat flux by 20%. Fourthly, the long-term change of SCSTF volume transport and its connection with the ocean circulation in the Pacific were discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.52173271,51922022 and 51773013)the Beijing Outstanding Young Scientist Program(Grant No.BJJWZYJH01201910010024)+3 种基金the China Postdoctoral Science Foundation(Grant Nos.2021T140044 and 2020M670110)the Beijing Municipal Natural Science Foundation(Grant No.2214074)the Beijing Municipal Science and Technology Project(Grant No.Z191100006619099)the Fundamental Research Funds for the Central Universities(Grant Nos.BHYC1705A and XK1802-2)。
文摘Metal-organic frameworks(MOFs)composed of functional metal ions/clusters and suitable bridging ligands are highly designable,which have shown excellent catalytic activity as nanozymes and are promising for antibacterial therapy.Herein,twodimensional(2D)copper MOF nanosheets(Cu-MOF NSs)as effective antibacterial agents were prepared through a simple onestep method.The 2D Cu-MOF NSs displayed a peroxidase-like activity toward H_(2)O_(2)decomposition into highly cytotoxic hydroxyl radicals(·OH).Notably,the 2D morphology of Cu-MOF NSs provides a high density of Cu^(2+)/Cu^(+)surface active sites,which could efficiently oxidize the proteins and lipids on the bacterial surface and induce the death of bacteria.It is found that the as-prepared 2D Cu-MOF NSs exhibited antibacterial properties against Staphylococcus aureus(S.aureus)and could efficiently eradicate the biofilm of S.aureus.Up to 99.9%bacteria were killed at a Cu-MOF concentration of 4μg/m L.This study opens a new avenue for the design of MOF-based antibacterial agents to combat pathogenic bacterial infections.
