We demonstrate a self-started,long-term stable polarization-maintaining mode-locked fiber laser based on the nonlinear polarization evolution technique.A polarized beam splitter is inserted into the cavity of the lin...We demonstrate a self-started,long-term stable polarization-maintaining mode-locked fiber laser based on the nonlinear polarization evolution technique.A polarized beam splitter is inserted into the cavity of the linear polarizationmaintaining fiber laser to facilitate self-started mode-locking.Pulses with single pulse energy of 26.9 nJ and average output power of 73.9 mW are obtained at the pump power of 600 mW.The transmission characteristics of artificial saturable absorber used in this laser are analyzed theoretically,the influence of the half-wave plate state on mode-locking is discussed,and the mode-locking range is obtained,which is well consistent with the experimental results.展开更多
Designing highly active and durable electrocatalysts towards oxygen reduction reaction(ORR)plays a paramount importance for proton exchange membrane fuel cells.Pt-based binary alloys Pt-M(M=3d-transition metals)posses...Designing highly active and durable electrocatalysts towards oxygen reduction reaction(ORR)plays a paramount importance for proton exchange membrane fuel cells.Pt-based binary alloys Pt-M(M=3d-transition metals)possessing excellent electronic and geometric properties have received increasing interests as highly active electrocatalysts.Herein,we report a series of Pt_(x)Co/C(x=1,2,3)catalysts by a facile one-pot soft-chemistry method.In the acidic conditions,the mass activities of PtCo/C,Pt_(2)Co/C and Pt_(3)Co/C are 0.526,0.462 and 0.441 A·mgPt^(-1),which are 2.60,2.31 and 2.22 times higher than that of Pt/C(0.200 A·mgPt^(-1)),respectively.The specific activities of PtCo/C,Pt_(2)Co/C and Pt_(3)Co/C are 706.59,679.41 and 801.83μA·cm^(-2),which are accordingly 2.89,2.76 and 3.28 times higher than that of Pt/C(244.75μA·cm^(-2)).Notably,Pt_(3)Co/C shows a remarkable durability.After 5000 cycles of the accelerated durability testing,the mass activity and specific activity of Pt_(3)Co/C catalyst are 2.47 and 3.80 times higher than that of the commercial Pt/C,respectively.The improved ORR activity and durability can be ascribed to the synergistic interaction between Pt and Co.展开更多
The key to use magnesium alloys as suitable biodegradable implants is how to adjust their degradation rates. We report a strategy to prepare biocompatible ceramic coating with improved biocorrosion resistance property...The key to use magnesium alloys as suitable biodegradable implants is how to adjust their degradation rates. We report a strategy to prepare biocompatible ceramic coating with improved biocorrosion resistance property on AZ91D alloy by microarc oxidation （MAO） in a silicate-K2ZrF6 solution with and without Ca（H2PO4）2 additives. The microstructure and biocorrosion of coatings were characterized by XRD and SEM, as well as electrochemical and immersion tests in simulated body fluid （SBF）. The results show that the coatings are mainly composed of MgO, Mg2SiO4, m-ZrO2 phases, further Ca containing compounds involve the coating by Ca（H2PO4）2 addition in the silicate-K2ZrF6 solution. The corrosion resistance of coated AZ91D alloy is significantly improved compared with the bare one. After immersing in SBF for 28 d, the Si-Zr5-CaO coating indicates a best corrosion resistance performance.展开更多
Aquatic vegetations widely exist in natural rivers and play an essential role in the evolution of the water environment and ecosystem by changing the river’s hydrodynamic characteristics and transporting sediments an...Aquatic vegetations widely exist in natural rivers and play an essential role in the evolution of the water environment and ecosystem by changing the river’s hydrodynamic characteristics and transporting sediments and nutrition.In reality,most aquatic vegetations are highly flexible,which invalidates the“rigid-cylinder”assumption widely adopted in many literatures.To explore the dynamics of submerged flexible vegetation in open-channel flows and its feedback to turbulent flow structures,numerical simulations are carried out using an in-house fluid-structure interaction(FSI)solver.In the simulations,the geometry of vegetation plants is grid-resolved,the turbulent flow is simulated using the large eddy simulation(LES),the dynamics of the flexible plants are solved using the vector form intrinsic finite element(VFIFE)method,and the turbulent flow and the plants are two-way coupled using the immersed boundary(IB)method.The dynamic responses of the flexible vegetation with different plant flexibility,spacing,and submergence are investigated.Simulation results show that flexible plants are subjected to complex flow-induced vibrations(FIVs)rather than static bending.The FIV involves both streamwise and cross-flow motions driven by the small-scale vortex shedding around the plants and the large-scale Kelvin-Helmholtz(K-H)vortices developed in the vegetation canopy layer.The vegetations exhibit pulsive wave motion of different patterns in relatively long and narrow open channels.Compared with the open-channel flows with static plants with equivalent bending deformation,the dynamic responses of flexible plants may increase the turbulent Reynolds stress of the open-channel flow by 70%–100%and increase the invasion depth of the K-H vortices by 30%–50%.展开更多
基金Project (2016B090931004) supported by the Scientific and Research Plan of Guangdong Province, ChinaProject (51601229) supported by the National Natural Science Foundation of China。
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61575011 and 61975003)the Beijing Natural Science Foundation,China(Grant No.4192015).
文摘We demonstrate a self-started,long-term stable polarization-maintaining mode-locked fiber laser based on the nonlinear polarization evolution technique.A polarized beam splitter is inserted into the cavity of the linear polarizationmaintaining fiber laser to facilitate self-started mode-locking.Pulses with single pulse energy of 26.9 nJ and average output power of 73.9 mW are obtained at the pump power of 600 mW.The transmission characteristics of artificial saturable absorber used in this laser are analyzed theoretically,the influence of the half-wave plate state on mode-locking is discussed,and the mode-locking range is obtained,which is well consistent with the experimental results.
基金financially supported by the Project of National Natural Science Foundation of China(No.5202780089)。
文摘Designing highly active and durable electrocatalysts towards oxygen reduction reaction(ORR)plays a paramount importance for proton exchange membrane fuel cells.Pt-based binary alloys Pt-M(M=3d-transition metals)possessing excellent electronic and geometric properties have received increasing interests as highly active electrocatalysts.Herein,we report a series of Pt_(x)Co/C(x=1,2,3)catalysts by a facile one-pot soft-chemistry method.In the acidic conditions,the mass activities of PtCo/C,Pt_(2)Co/C and Pt_(3)Co/C are 0.526,0.462 and 0.441 A·mgPt^(-1),which are 2.60,2.31 and 2.22 times higher than that of Pt/C(0.200 A·mgPt^(-1)),respectively.The specific activities of PtCo/C,Pt_(2)Co/C and Pt_(3)Co/C are 706.59,679.41 and 801.83μA·cm^(-2),which are accordingly 2.89,2.76 and 3.28 times higher than that of Pt/C(244.75μA·cm^(-2)).Notably,Pt_(3)Co/C shows a remarkable durability.After 5000 cycles of the accelerated durability testing,the mass activity and specific activity of Pt_(3)Co/C catalyst are 2.47 and 3.80 times higher than that of the commercial Pt/C,respectively.The improved ORR activity and durability can be ascribed to the synergistic interaction between Pt and Co.
基金Acknowledgements The partial supports from the National Natural Science Foundation of China （NSFC Grant Nos. 51371071, 51321061 and 51275555）, the National Basic Science Research Program （Grant No. 2012CB933900）, the Fundamental Research Funds for the Central Universities （HIT.BRETIII.201202） and the Program for New Century Excellent Talents in University of China （NCET-08-0166） are gratefully acknowledged.
文摘The key to use magnesium alloys as suitable biodegradable implants is how to adjust their degradation rates. We report a strategy to prepare biocompatible ceramic coating with improved biocorrosion resistance property on AZ91D alloy by microarc oxidation （MAO） in a silicate-K2ZrF6 solution with and without Ca（H2PO4）2 additives. The microstructure and biocorrosion of coatings were characterized by XRD and SEM, as well as electrochemical and immersion tests in simulated body fluid （SBF）. The results show that the coatings are mainly composed of MgO, Mg2SiO4, m-ZrO2 phases, further Ca containing compounds involve the coating by Ca（H2PO4）2 addition in the silicate-K2ZrF6 solution. The corrosion resistance of coated AZ91D alloy is significantly improved compared with the bare one. After immersing in SBF for 28 d, the Si-Zr5-CaO coating indicates a best corrosion resistance performance.
基金the National Natural Science Foundation of China(Grant Nos.5217090155,51979186 and 51779175).
文摘Aquatic vegetations widely exist in natural rivers and play an essential role in the evolution of the water environment and ecosystem by changing the river’s hydrodynamic characteristics and transporting sediments and nutrition.In reality,most aquatic vegetations are highly flexible,which invalidates the“rigid-cylinder”assumption widely adopted in many literatures.To explore the dynamics of submerged flexible vegetation in open-channel flows and its feedback to turbulent flow structures,numerical simulations are carried out using an in-house fluid-structure interaction(FSI)solver.In the simulations,the geometry of vegetation plants is grid-resolved,the turbulent flow is simulated using the large eddy simulation(LES),the dynamics of the flexible plants are solved using the vector form intrinsic finite element(VFIFE)method,and the turbulent flow and the plants are two-way coupled using the immersed boundary(IB)method.The dynamic responses of the flexible vegetation with different plant flexibility,spacing,and submergence are investigated.Simulation results show that flexible plants are subjected to complex flow-induced vibrations(FIVs)rather than static bending.The FIV involves both streamwise and cross-flow motions driven by the small-scale vortex shedding around the plants and the large-scale Kelvin-Helmholtz(K-H)vortices developed in the vegetation canopy layer.The vegetations exhibit pulsive wave motion of different patterns in relatively long and narrow open channels.Compared with the open-channel flows with static plants with equivalent bending deformation,the dynamic responses of flexible plants may increase the turbulent Reynolds stress of the open-channel flow by 70%–100%and increase the invasion depth of the K-H vortices by 30%–50%.
