High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically pol...High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate(PPLN) part and an aperiodically poled lithium niobate(APPLN) part.Two infrared pump waves with a frequency difference ω_(T1) generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation(CDFG).The generated cascaded optical waves with frequency interval ω_(T1) then further interact in the APPLN part by OCDFG,yielding the following two advantages.First,OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves,yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K.Second,THz waves with M timesω_(T1) are generated by mixing the mth-order and the(m+M)th-order cascaded optical waves by designing poling period distributions of the APPLN part.展开更多
A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded differe...A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.展开更多
Multicomputer systems(distributed memory computer systems) are becoming more and more popular and will be wildly used in scientific researches. In this paper, we present a parallel algorithm of Fourier Transform of a ...Multicomputer systems(distributed memory computer systems) are becoming more and more popular and will be wildly used in scientific researches. In this paper, we present a parallel algorithm of Fourier Transform of a vector of complex numbers on multicomputer system and give its computing times and its speedup in parallel environment supported by EXPRESS system on the multicomputer system which consists of four SGI workstations. Our analysis shows that the results is ideal and this scheme is suitable to multicomputer systems.展开更多
Synthesizing bimetallic nanomaterials,with noble metals as the surface layers and inert metals as the substrates,has been proven to be an effective way to reduce the use of noble metals with maintained catalytic activ...Synthesizing bimetallic nanomaterials,with noble metals as the surface layers and inert metals as the substrates,has been proven to be an effective way to reduce the use of noble metals with maintained catalytic activity.However,an atomic diffusion from the inert substrate to the surface during the long-term operation has been reported to significantly decrease the activity.In this work,a series of catalysis-inert Cu-coated Ni foil were fabricated through electrodeposition and their activities for alkaline hydrogen evolution were investigated.Notably,the Ni/Cu-60 sample showed a similar catalytic property with pure Ni foil and only a slight decrease in HER activity was observed.The X-ray photoelectron spectroscopy(XPS)results indicated a decreased electron concentration of Cu in Ni/Cu-60,and theoretical calculations further demonstrated the electron transfer between the Ni substrate and Cu layer.Our results reveal that a specific composition or structure of an inert metal layer might not significantly decrease the electrocatalytic activity of active metals.Moreover,there are more possibilities for the rational design of metal-based catalysts for electrocatalysis.展开更多
Developing inexpensive and high efficient catalysts is essential for generating oxygen and hydrogen via water splitting.Herein,based on powder metallurgy,a Ni-Fe based compound(Ni8Fe2 alloy)with unique porous structur...Developing inexpensive and high efficient catalysts is essential for generating oxygen and hydrogen via water splitting.Herein,based on powder metallurgy,a Ni-Fe based compound(Ni8Fe2 alloy)with unique porous structure and controllable phase has been designed and synthesized.Without using a solvent or template,the alloy exhibits a porous structure with uniformly distributed multi-phase.The obtained Ni8Fe2 alloy exhibits an efficient oxygen evolution reaction(OER)performance and good longterm stability in alkaline electrolyte(i.e.1.0 M KOH).Additionally,an alkaline water splitting device has been assembled using porous Ni8Fe2 alloy as both anode and cathode materials.The system requires a cell voltage of 1.65 V to reach the 10 mA cm-2 current density for overall water splitting and maintains good stability for 25 h.The efficient electrocatalytic performance of the Ni8Fe2 alloy is owing to the unique porous microstructure,increased active sites and accelerated charge transfer.Consequently,the reaction kinetics of OER are significantly promoted.展开更多
Sluggish water dissociation kinetics severely limits the rate of alkaline electrocatalytic hydrogen evolution reaction(HER).Therefore,finding highly active electrocatalysts and clarifying the mechanism of water dissoc...Sluggish water dissociation kinetics severely limits the rate of alkaline electrocatalytic hydrogen evolution reaction(HER).Therefore,finding highly active electrocatalysts and clarifying the mechanism of water dissociation are challenging but important.In this study,we report an integrated nanoporous nickel(np-Ni)catalyst with high alkaline HER performance and the origin of the corresponding enhanced catalytic activity.In 1 mol L^(-1) KOH solution,this np-Ni electrode shows an HER overpotential of 20 mV at 10 mA cm^(-2),along with fast water dissociation kinetics.The excellent performance is not only attributed to the large surface area provided by the three-dimensional interconnected conductive network but also from the enhanced intrinsic activity induced by the unique surface properties.Further studies reveal that the types of oxygen species that naturally form on the Ni surface play a key role in water dissociation.Remarkably,when the lattice oxygen almost disappears,the Ni surface terminates with_(ads)orbed oxygen(O_(ads)),exhibiting the fastest water dissociation kinetics.Density functional theory calculation suggests that when O_(ads)acts as the surface termination of Ni metal,the orientation and configuration of polar water molecules are strongly affected by O_(ads).Finally,the H–OH bond of interfacial water molecules is effectively activated in a manner similar to hydrogen bonding.This work not only identifies a high-performance and low-cost electrocatalyst but also provides new insights into the chemical processes underlying water dissociation,thus benefiting the rational design of electrocatalysts.展开更多
ABSTRACT Introduction:Antimicrobial resistance has become a major public health threat globally.The prevalence of multidrug-resistant(MDR)bacterial infections increased substantially among inpatients under 18 years of...ABSTRACT Introduction:Antimicrobial resistance has become a major public health threat globally.The prevalence of multidrug-resistant(MDR)bacterial infections increased substantially among inpatients under 18 years of age in recent years.In Zhejiang Province,China,the trends of drug-resistance in non-adult patients from 2014 to 2019 were monitored,aiming to determine the variation patterns and epidemiological features of MDR strains.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)the Natural Science Foundation of Henan Province,China(Grant No.162300410190)Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate(PPLN) part and an aperiodically poled lithium niobate(APPLN) part.Two infrared pump waves with a frequency difference ω_(T1) generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation(CDFG).The generated cascaded optical waves with frequency interval ω_(T1) then further interact in the APPLN part by OCDFG,yielding the following two advantages.First,OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves,yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K.Second,THz waves with M timesω_(T1) are generated by mixing the mth-order and the(m+M)th-order cascaded optical waves by designing poling period distributions of the APPLN part.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)Natural Science Foundation of Henan Province,China(Grant No.162300410190)Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.
文摘Multicomputer systems(distributed memory computer systems) are becoming more and more popular and will be wildly used in scientific researches. In this paper, we present a parallel algorithm of Fourier Transform of a vector of complex numbers on multicomputer system and give its computing times and its speedup in parallel environment supported by EXPRESS system on the multicomputer system which consists of four SGI workstations. Our analysis shows that the results is ideal and this scheme is suitable to multicomputer systems.
基金supported by the National Natural Science Foun-dation of China(Nos.52231008 and 52001227).
文摘Synthesizing bimetallic nanomaterials,with noble metals as the surface layers and inert metals as the substrates,has been proven to be an effective way to reduce the use of noble metals with maintained catalytic activity.However,an atomic diffusion from the inert substrate to the surface during the long-term operation has been reported to significantly decrease the activity.In this work,a series of catalysis-inert Cu-coated Ni foil were fabricated through electrodeposition and their activities for alkaline hydrogen evolution were investigated.Notably,the Ni/Cu-60 sample showed a similar catalytic property with pure Ni foil and only a slight decrease in HER activity was observed.The X-ray photoelectron spectroscopy(XPS)results indicated a decreased electron concentration of Cu in Ni/Cu-60,and theoretical calculations further demonstrated the electron transfer between the Ni substrate and Cu layer.Our results reveal that a specific composition or structure of an inert metal layer might not significantly decrease the electrocatalytic activity of active metals.Moreover,there are more possibilities for the rational design of metal-based catalysts for electrocatalysis.
基金supported financially by the National Natural Science Foundation of China(Nos.51571151,51701139,51671143 and U1601216).
文摘Developing inexpensive and high efficient catalysts is essential for generating oxygen and hydrogen via water splitting.Herein,based on powder metallurgy,a Ni-Fe based compound(Ni8Fe2 alloy)with unique porous structure and controllable phase has been designed and synthesized.Without using a solvent or template,the alloy exhibits a porous structure with uniformly distributed multi-phase.The obtained Ni8Fe2 alloy exhibits an efficient oxygen evolution reaction(OER)performance and good longterm stability in alkaline electrolyte(i.e.1.0 M KOH).Additionally,an alkaline water splitting device has been assembled using porous Ni8Fe2 alloy as both anode and cathode materials.The system requires a cell voltage of 1.65 V to reach the 10 mA cm-2 current density for overall water splitting and maintains good stability for 25 h.The efficient electrocatalytic performance of the Ni8Fe2 alloy is owing to the unique porous microstructure,increased active sites and accelerated charge transfer.Consequently,the reaction kinetics of OER are significantly promoted.
基金supported by the National Natural Science Foundation of China(51571151,51701139,51671143,52177220,and 51804216)。
文摘Sluggish water dissociation kinetics severely limits the rate of alkaline electrocatalytic hydrogen evolution reaction(HER).Therefore,finding highly active electrocatalysts and clarifying the mechanism of water dissociation are challenging but important.In this study,we report an integrated nanoporous nickel(np-Ni)catalyst with high alkaline HER performance and the origin of the corresponding enhanced catalytic activity.In 1 mol L^(-1) KOH solution,this np-Ni electrode shows an HER overpotential of 20 mV at 10 mA cm^(-2),along with fast water dissociation kinetics.The excellent performance is not only attributed to the large surface area provided by the three-dimensional interconnected conductive network but also from the enhanced intrinsic activity induced by the unique surface properties.Further studies reveal that the types of oxygen species that naturally form on the Ni surface play a key role in water dissociation.Remarkably,when the lattice oxygen almost disappears,the Ni surface terminates with_(ads)orbed oxygen(O_(ads)),exhibiting the fastest water dissociation kinetics.Density functional theory calculation suggests that when O_(ads)acts as the surface termination of Ni metal,the orientation and configuration of polar water molecules are strongly affected by O_(ads).Finally,the H–OH bond of interfacial water molecules is effectively activated in a manner similar to hydrogen bonding.This work not only identifies a high-performance and low-cost electrocatalyst but also provides new insights into the chemical processes underlying water dissociation,thus benefiting the rational design of electrocatalysts.
文摘ABSTRACT Introduction:Antimicrobial resistance has become a major public health threat globally.The prevalence of multidrug-resistant(MDR)bacterial infections increased substantially among inpatients under 18 years of age in recent years.In Zhejiang Province,China,the trends of drug-resistance in non-adult patients from 2014 to 2019 were monitored,aiming to determine the variation patterns and epidemiological features of MDR strains.
