Upper turbulent mixing in the interior and surrounding areas of an anticyclonic eddy in the northern South China Sea(SCS)was estimated from underwater glider data(May 2015)in the present study,using the Gregg-HenyeyPo...Upper turbulent mixing in the interior and surrounding areas of an anticyclonic eddy in the northern South China Sea(SCS)was estimated from underwater glider data(May 2015)in the present study,using the Gregg-HenyeyPolzin parameterization and the Thorpe-scale method.The observations revealed a clear asymmetrical spatial pattern of turbulent mixing in the anticyclonic eddy area.Enhanced diffusivity(in the order of 10–3 m2/s)was found at the posterior edge of the anticyclonic mesoscale eddy;on the anterior side,diffusivity was one order of magnitude lower on average.This asymmetrical pattern was highly correlated with the eddy kinetic energy.Higher shear variance on the posterior side,which is conducive to the triggering of shear instability,may be the main mechanism for the elevated diffusivity.In addition,the generation and growth of sub-mesoscale motions that are fed by mesoscale eddies on their posterior side may also promote the occurrence of strong mixing in the studied region.The results of this study help improve our knowledge regarding turbulent mixing in the northern SCS.展开更多
In this work,the A356/AZ91D bimetal composites were prepared by ultrasonic vibration-assisted lost foam compound casting,and the effects of ultrasonic powers on interfacial microstructures and mechan-ical properties o...In this work,the A356/AZ91D bimetal composites were prepared by ultrasonic vibration-assisted lost foam compound casting,and the effects of ultrasonic powers on interfacial microstructures and mechan-ical properties of the Al/Mg interfaces were investigated.Results revealed that the Al/Mg bimetal com-posites without ultrasonic vibration treatment(UVT)were heterogeneous,and the Al/Mg interface was composed of Al-Mg intermetallic compounds(IMCs,i.e.,Al_(3)Mg_(2)and Al_(12)Mg_(17))area and Al-Mg eutec-tic structures(δ-Mg+Al_(12)Mg_(17))area.The Mg_(2)Si particles were gathered at the IMCs area and an oxide film that mainly composed of Al_(2)O_(3)was existed between the IMCs area and eutectic structures area.With UVT,the oxide film was eliminated and the gathered Mg_(2)Si particles were refined and dispersed by the acoustic cavitation effect,and part of the Al_(3)Mg_(2)and Al-Mg eutectic structures were transformed into the Al_(12)Mg_(17)due to the promoted solute interdiffusion,which improved the homogeneity of the Al/Mg interfaces.Besides,the grains of the Al/Mg interface with UVT under ultrasonic power of 75 W were significantly refined.The thickness of Al/Mg interface was increased with the increase of the ul-trasonic power.Due to the excessive heat induced by UVT under the further increased ultrasonic power,the cooling rates and the degree of supercooling were reduced,resulting in the coarsening of interfacial grains.The microhardness of the Al/Mg interfaces was increased and got more uniform by UVT.The shear strengths of the Al/Mg bimetal composites with UVT were enhanced to 61.4 MPa from 32.4 MPa,with an increase of 89.5%compared with that of the Al/Mg bimetal without UVT.This could be ascribed to the removal of the oxide film,the refinement of the interfacial grains and the dispersed and refined Mg_(2)Si particles achieved by UVT,which hindered the crack propagation during deformation.展开更多
Lithium-sulfur batteries(LSBs)are considered as the next generation of advanced rechargeable batteries because of their high energy density.In this study,sulfur and CoxS electrocatalyst are deposited on carbon nanotub...Lithium-sulfur batteries(LSBs)are considered as the next generation of advanced rechargeable batteries because of their high energy density.In this study,sulfur and CoxS electrocatalyst are deposited on carbon nanotube buckypaper(S/CoxS/BP)by a facile electrodeposition method and are used as a binder-free high-performance cathode for LSBs.Elemental sulfur is deposited on buckypaper by electrooxidation of a polysulfide solution(-S6^2-).This approach substantially increased the current and time efficiency of sulfur electrochemical deposition on conductive material for LSBs.S/CoxS/BP cathode could deliver an initial discharge capacity as high as 1650 mAh g^-1 at 0.1 C,which is close to the theoretical capacity of sulfur.At current rate of 0.5 C,the S/CoxS/BP has a capacity of 1420 mAh g^-1 at the first cycle and 715 mAh g^-1 after 500 cycles with a fading rate of 0.099%per cycle.The high capacity of S/CoxS/BP is attributed to both the homogeneous dispersion of nanosized sulfur within BP and the presence of CoxS catalyst.The sodium dodecyl sulfate(SDS)pretreatment of BP renders it polarity to bind polysulfides and thus facilitates the good dispersibility of nanosized sulfur within BP.CoxS catalyst accelerates the kinetics of polysulfide conversion and reduces the presence of polysulfide in the cathode,which suppresses the polysulfide diffusion to anode,i.e.,the shuttle effect.The mitigation of the active material loss improves not only the capacity but also the cyclability of S/CoxS/BP.展开更多
Carbonate electrolytes are one of the most desirable electrolytes for high-energy lithium-sulfur batteries(LSBs)because of their successful implementation in commercial Li-ion batteries.The low-polysulfide-solubility ...Carbonate electrolytes are one of the most desirable electrolytes for high-energy lithium-sulfur batteries(LSBs)because of their successful implementation in commercial Li-ion batteries.The low-polysulfide-solubility feature of some carbonate solvents also makes them very promising for overcoming the shuttle effects of LSBs.However,regular sulfur electrodes experience undesired electrochemical mechanisms in carbonate electrolytes due to side reactions.In this study,we report a catalytic redox mechanism of sulfur in propylene carbonate(PC)electrolyte based on a compari-son study.The catalytic mechanism is characterized by the interactions between polysulfides and dual N/O functional groups on the host carbon,which largely prevents side reactions between polysulfides and the carbonate electrolyte.Such a mechanism coupled with the low-polysulfide-solubility feature leads to stable cycling of LSBs in PC electrolyte.Favorable dual N/O functional groups are identified via a density functional theory study.This work provides an alternative route for enabling LSBs in carbonate electrolytes.展开更多
Turbulent eddies play a critical role in oceanic flows. Direct measurements of turbulent eddy fluxes beneath the sea surface were taken to study the direction of flux-carrying eddies as a means of supplementing our un...Turbulent eddies play a critical role in oceanic flows. Direct measurements of turbulent eddy fluxes beneath the sea surface were taken to study the direction of flux-carrying eddies as a means of supplementing our understanding of vertical fluxes exchange processes and their relationship to tides. The observations were made at 32 Hz at a water depth of ~1.5 m near the coast of Sanya, China, using an eddy covariance system, which mainly consists of an acoustic doppler velocimeter(ADV) and a fast temperature sensor. The cospectra-fit method-an established semi-empirical model of boundary layer turbulence to the measured turbulent cospectra at frequencies below those of surface gravity waves-was used in the presence of surface gravity waves to quantify the turbulent eddy fluxes(including turbulent heat flux and Reynolds stress). As much as 87% of the total turbulent stress and 88% of the total turbulent heat flux were determined as being at band frequencies below those of surface gravity waves. Both the turbulent heat flux and Reynolds stress showed a daily successive variation;the former peaked during the low tide period and the later peaked during the ebb tide period.Estimation of roll-off wavenumbers, k0, and roll-off wavelengths, λ0(where λ0=2π/k0), which were estimated as the horizontal length scales of the dominant flux-carrying turbulent eddies, indicated that the λ0 of the turbulent heat flux was approximately double that of the Reynolds stress. Wavelet analysis showed that both the turbulent heat flux and the Reynolds stress have a close relationship to the semi-diurnal and diurnal tides, and therefore indicate the energy that is transported from tides to turbulence.展开更多
Various factors can induce cell degeneration by altering the phenotype and metabolism of cells.Mitochondria play an essential role in cellular homeostasis and function,rendering aging processes highly associated with ...Various factors can induce cell degeneration by altering the phenotype and metabolism of cells.Mitochondria play an essential role in cellular homeostasis and function,rendering aging processes highly associated with mitochondrial function and status.Herein,we describe an aging-prone phenotype of murine skin cells caused by depletion of Rad6B(Ube2b),an E2 ubiquitin-conjugating enzyme.In this study,using Masson’s trichrome,we showed that loss of Rad6B causes physiological structure changes in mouse skin with age.In addition,a combination of western blotting experiments,transmission electron microscopy and employment of immunofluorescence staining revealed that depletion of Rad6B was characterized by an abnormal mitochondrial metabolic profile,including decreased mitochondrial biosynthesis and mitochondrial complex activities,increased ROS production and suppressed mitophagy resulting in metabolic disorders.Taken together,these results highlight an important relationship between Rad6B and skin senescence,suggesting that Rad6B plays an indispensable role in maintaining a healthy mitochondrial network and intracellular homeostasis.展开更多
Coating commercial porous polyolefin separators with inorganic materials can improve the thermal stability of the polyolefin separators and hence improve the safety of lithium-ion batteries. Several different inorgani...Coating commercial porous polyolefin separators with inorganic materials can improve the thermal stability of the polyolefin separators and hence improve the safety of lithium-ion batteries. Several different inorganic materials have been studied for the coating. However, there lacks a study on how different the properties of separators, in inorganic materials affect terms of thermal stability and cell performance. Herein, we present such a study on coating a commercial polypropylene separator with four inorganic materials, i.e., Al2O3, SiO2, ZrO2 and zeolite. All inorganic coatings have improved thermal stability of the separators although with differences. The coating layers add 28%-45% of electrical resistance compared with the pure polypropylene separator, but all the cells prepared with the coated polypropylene separators have the same electrical chemical performance as the uncoated separator in terms of rate capability and capacities at different temperatures.展开更多
The evaluation of the intrinsic activity of catalysts is the most basic in searching energy-and cost-efficient catalyst materials for various applications.The accurate determination of the intrinsic activity is essent...The evaluation of the intrinsic activity of catalysts is the most basic in searching energy-and cost-efficient catalyst materials for various applications.The accurate determination of the intrinsic activity is essential for identifying efficient catalysts.While a huge number of studies of electrocatalysis for various applications have been reported,the effects of electrode loading on the apparent intrinsic activity obtained experimentally have been rarely discussed.With a high mass loading on the electrode,not all the catalyst surfaces can be electrochemically active because not all the surfaces can be wetted by the electrolyte.The loading also affects the transport of electrons over the electrode as well as the transport of ions in the electrolyte,and thus affects the kinetics.These lead to the derivations of the apparent intrinsic activity from the real intrinsic activity.Herein,for better understanding the derivations,we evaluate and discuss the effects of electrode mass loading using oxygen evolution reaction as an example.展开更多
基金The National Key R&D Plan of China under contract Nos 2017YFC0305904,2017YFC0305804 and 2016YFC1401404the National Natural Science Foundation of China under contract Nos 41876023,41630970,41806037,41706137 and 41806033+4 种基金the Guangdong Science and Technology Project under contract Nos 2019A1515111044,2018A0303130047 and 2017A030310332the Guangzhou Science and Technology Project under contract No.201707020037the Natural Science Foundation of Shenzhen University under contract No.2019078the Dedicated Fund for Promoting High-quality Economic Development in Guangdong Province(Marine Economic Development Project)under contract No.GDOE2019A03the Independent Research Project Program of State Key Laboratory of Tropical Oceanography under contract Nos LTOZZ1902 and LTO1909。
文摘Upper turbulent mixing in the interior and surrounding areas of an anticyclonic eddy in the northern South China Sea(SCS)was estimated from underwater glider data(May 2015)in the present study,using the Gregg-HenyeyPolzin parameterization and the Thorpe-scale method.The observations revealed a clear asymmetrical spatial pattern of turbulent mixing in the anticyclonic eddy area.Enhanced diffusivity(in the order of 10–3 m2/s)was found at the posterior edge of the anticyclonic mesoscale eddy;on the anterior side,diffusivity was one order of magnitude lower on average.This asymmetrical pattern was highly correlated with the eddy kinetic energy.Higher shear variance on the posterior side,which is conducive to the triggering of shear instability,may be the main mechanism for the elevated diffusivity.In addition,the generation and growth of sub-mesoscale motions that are fed by mesoscale eddies on their posterior side may also promote the occurrence of strong mixing in the studied region.The results of this study help improve our knowledge regarding turbulent mixing in the northern SCS.
基金supported by the National Natural Science Foundation of China(Nos.52271102 and 52075198)the National Key Research and Development Program of China(No.2020YFB2008304),and the Analytical and Testing Center,HUST。
文摘In this work,the A356/AZ91D bimetal composites were prepared by ultrasonic vibration-assisted lost foam compound casting,and the effects of ultrasonic powers on interfacial microstructures and mechan-ical properties of the Al/Mg interfaces were investigated.Results revealed that the Al/Mg bimetal com-posites without ultrasonic vibration treatment(UVT)were heterogeneous,and the Al/Mg interface was composed of Al-Mg intermetallic compounds(IMCs,i.e.,Al_(3)Mg_(2)and Al_(12)Mg_(17))area and Al-Mg eutec-tic structures(δ-Mg+Al_(12)Mg_(17))area.The Mg_(2)Si particles were gathered at the IMCs area and an oxide film that mainly composed of Al_(2)O_(3)was existed between the IMCs area and eutectic structures area.With UVT,the oxide film was eliminated and the gathered Mg_(2)Si particles were refined and dispersed by the acoustic cavitation effect,and part of the Al_(3)Mg_(2)and Al-Mg eutectic structures were transformed into the Al_(12)Mg_(17)due to the promoted solute interdiffusion,which improved the homogeneity of the Al/Mg interfaces.Besides,the grains of the Al/Mg interface with UVT under ultrasonic power of 75 W were significantly refined.The thickness of Al/Mg interface was increased with the increase of the ul-trasonic power.Due to the excessive heat induced by UVT under the further increased ultrasonic power,the cooling rates and the degree of supercooling were reduced,resulting in the coarsening of interfacial grains.The microhardness of the Al/Mg interfaces was increased and got more uniform by UVT.The shear strengths of the Al/Mg bimetal composites with UVT were enhanced to 61.4 MPa from 32.4 MPa,with an increase of 89.5%compared with that of the Al/Mg bimetal without UVT.This could be ascribed to the removal of the oxide film,the refinement of the interfacial grains and the dispersed and refined Mg_(2)Si particles achieved by UVT,which hindered the crack propagation during deformation.
基金conducted by Nanomaterials for Energy and Energy-Water Nexus(NEW)Programme under Singapore-HUJ Alliance for Research and Enterprise(SHARE)in the Campus for Research Excellence and Technological Enterprise(CREATE)that is supported by the National Research Foundation,Prime Minister’s O ce,Singaporesupported also by the Israel National Research Center for Electrochemical Propulsion(INREP)。
文摘Lithium-sulfur batteries(LSBs)are considered as the next generation of advanced rechargeable batteries because of their high energy density.In this study,sulfur and CoxS electrocatalyst are deposited on carbon nanotube buckypaper(S/CoxS/BP)by a facile electrodeposition method and are used as a binder-free high-performance cathode for LSBs.Elemental sulfur is deposited on buckypaper by electrooxidation of a polysulfide solution(-S6^2-).This approach substantially increased the current and time efficiency of sulfur electrochemical deposition on conductive material for LSBs.S/CoxS/BP cathode could deliver an initial discharge capacity as high as 1650 mAh g^-1 at 0.1 C,which is close to the theoretical capacity of sulfur.At current rate of 0.5 C,the S/CoxS/BP has a capacity of 1420 mAh g^-1 at the first cycle and 715 mAh g^-1 after 500 cycles with a fading rate of 0.099%per cycle.The high capacity of S/CoxS/BP is attributed to both the homogeneous dispersion of nanosized sulfur within BP and the presence of CoxS catalyst.The sodium dodecyl sulfate(SDS)pretreatment of BP renders it polarity to bind polysulfides and thus facilitates the good dispersibility of nanosized sulfur within BP.CoxS catalyst accelerates the kinetics of polysulfide conversion and reduces the presence of polysulfide in the cathode,which suppresses the polysulfide diffusion to anode,i.e.,the shuttle effect.The mitigation of the active material loss improves not only the capacity but also the cyclability of S/CoxS/BP.
文摘Carbonate electrolytes are one of the most desirable electrolytes for high-energy lithium-sulfur batteries(LSBs)because of their successful implementation in commercial Li-ion batteries.The low-polysulfide-solubility feature of some carbonate solvents also makes them very promising for overcoming the shuttle effects of LSBs.However,regular sulfur electrodes experience undesired electrochemical mechanisms in carbonate electrolytes due to side reactions.In this study,we report a catalytic redox mechanism of sulfur in propylene carbonate(PC)electrolyte based on a compari-son study.The catalytic mechanism is characterized by the interactions between polysulfides and dual N/O functional groups on the host carbon,which largely prevents side reactions between polysulfides and the carbonate electrolyte.Such a mechanism coupled with the low-polysulfide-solubility feature leads to stable cycling of LSBs in PC electrolyte.Favorable dual N/O functional groups are identified via a density functional theory study.This work provides an alternative route for enabling LSBs in carbonate electrolytes.
基金The National Natural Science Foundation of China under contract Nos 41876023, 41630970 and 41876022the Instrument Developing Project of the Chinese Academy of Sciences under contract No. YZ201432+1 种基金the Guangzhou Science and Technology Project under contract No. 201707020037the National Key R&D Plan of China under contract Nos 2017YFC0305804 and 2017YFC0305904.
文摘Turbulent eddies play a critical role in oceanic flows. Direct measurements of turbulent eddy fluxes beneath the sea surface were taken to study the direction of flux-carrying eddies as a means of supplementing our understanding of vertical fluxes exchange processes and their relationship to tides. The observations were made at 32 Hz at a water depth of ~1.5 m near the coast of Sanya, China, using an eddy covariance system, which mainly consists of an acoustic doppler velocimeter(ADV) and a fast temperature sensor. The cospectra-fit method-an established semi-empirical model of boundary layer turbulence to the measured turbulent cospectra at frequencies below those of surface gravity waves-was used in the presence of surface gravity waves to quantify the turbulent eddy fluxes(including turbulent heat flux and Reynolds stress). As much as 87% of the total turbulent stress and 88% of the total turbulent heat flux were determined as being at band frequencies below those of surface gravity waves. Both the turbulent heat flux and Reynolds stress showed a daily successive variation;the former peaked during the low tide period and the later peaked during the ebb tide period.Estimation of roll-off wavenumbers, k0, and roll-off wavelengths, λ0(where λ0=2π/k0), which were estimated as the horizontal length scales of the dominant flux-carrying turbulent eddies, indicated that the λ0 of the turbulent heat flux was approximately double that of the Reynolds stress. Wavelet analysis showed that both the turbulent heat flux and the Reynolds stress have a close relationship to the semi-diurnal and diurnal tides, and therefore indicate the energy that is transported from tides to turbulence.
基金funded by the National Natural Science Foundation of China(Grant Nos.82071695 and 81772907 to DW and No.82060535 to YT)the Fundamental Research Funds for the Central Universities(Grant lzujbky-2017-k12 to DW).
文摘Various factors can induce cell degeneration by altering the phenotype and metabolism of cells.Mitochondria play an essential role in cellular homeostasis and function,rendering aging processes highly associated with mitochondrial function and status.Herein,we describe an aging-prone phenotype of murine skin cells caused by depletion of Rad6B(Ube2b),an E2 ubiquitin-conjugating enzyme.In this study,using Masson’s trichrome,we showed that loss of Rad6B causes physiological structure changes in mouse skin with age.In addition,a combination of western blotting experiments,transmission electron microscopy and employment of immunofluorescence staining revealed that depletion of Rad6B was characterized by an abnormal mitochondrial metabolic profile,including decreased mitochondrial biosynthesis and mitochondrial complex activities,increased ROS production and suppressed mitophagy resulting in metabolic disorders.Taken together,these results highlight an important relationship between Rad6B and skin senescence,suggesting that Rad6B plays an indispensable role in maintaining a healthy mitochondrial network and intracellular homeostasis.
文摘Coating commercial porous polyolefin separators with inorganic materials can improve the thermal stability of the polyolefin separators and hence improve the safety of lithium-ion batteries. Several different inorganic materials have been studied for the coating. However, there lacks a study on how different the properties of separators, in inorganic materials affect terms of thermal stability and cell performance. Herein, we present such a study on coating a commercial polypropylene separator with four inorganic materials, i.e., Al2O3, SiO2, ZrO2 and zeolite. All inorganic coatings have improved thermal stability of the separators although with differences. The coating layers add 28%-45% of electrical resistance compared with the pure polypropylene separator, but all the cells prepared with the coated polypropylene separators have the same electrical chemical performance as the uncoated separator in terms of rate capability and capacities at different temperatures.
基金The work was partially supported by the Singapore Ministry of Education Tier 1 Grant(2019-T1-002-125)Dr.S.Sun thanks the funding support from Beijing Natural Science Foundation Program 2212029 and National Natural Science Foundation of China-Youth Science Fund(Grant No.52001009)Dr.Yu thanks the financial support from the National Research Foundation,Prime Minister's Office,Singapore,under its Campus for Research Excellence and Technological Enterprise(CREATE)program。
文摘The evaluation of the intrinsic activity of catalysts is the most basic in searching energy-and cost-efficient catalyst materials for various applications.The accurate determination of the intrinsic activity is essential for identifying efficient catalysts.While a huge number of studies of electrocatalysis for various applications have been reported,the effects of electrode loading on the apparent intrinsic activity obtained experimentally have been rarely discussed.With a high mass loading on the electrode,not all the catalyst surfaces can be electrochemically active because not all the surfaces can be wetted by the electrolyte.The loading also affects the transport of electrons over the electrode as well as the transport of ions in the electrolyte,and thus affects the kinetics.These lead to the derivations of the apparent intrinsic activity from the real intrinsic activity.Herein,for better understanding the derivations,we evaluate and discuss the effects of electrode mass loading using oxygen evolution reaction as an example.
