Na_(3)V_(2)(PO_(4))_(2)O_(2)F(NVPOF)has received considerable interest as a promising cathode material for sodium-ion batteries because of its high working voltage and good structural/thermal stability.However,the slu...Na_(3)V_(2)(PO_(4))_(2)O_(2)F(NVPOF)has received considerable interest as a promising cathode material for sodium-ion batteries because of its high working voltage and good structural/thermal stability.However,the sluggish electrode reaction resulting from its low intrinsic electronic conductivity significantly restricts its electrochemical performance and thus its practical application.Herein,Nb-doped Na_(3)V_(2-x)Nb_(x)(PO_(4))_(2)O_(2)F/graphene(rGO)composites(x=0,0.05,0.1)were prepared using a solvothermal method followed by calcination.Compared to the un-doped NVPOF/r GO,doping V-site with high-valence Nb element(Nb^(5+))(Na_(3)V_(1.95)Nb_(0.05)(PO_(4))_(2)O_(2)F/r GO(NVN05POF/rGO))can result in the generated V4^(+)/V3^(+)mixed-valence,ensuring the lower bandgap and thus the increased intrinsic electronic conductivity.Besides,the expanded lattice space favors the Na^(+)migration.With the structure feature where NVN05POF particles are attached to the rGO sheets,the electrode reaction kinetics is further accelerated owing to the well-constructed electron conductive network.As a consequence,the as-prepared NVN05POF/r GO sample exhibits a high specific capacity of~72 m Ah·g^(-1)at 10C(capacity retention of 65.2%(vs.0.5C))and excellent long-term cycling stability with the capacity fading rate of~0.099%per cycle in 500 cycles at 5C.展开更多
Silicon suboxide(SiO_(x),0<x<2)is recognized as one of the next-generation anode materials for high-energy-density lithium ion batteries(LIBs)due to its high theoretical specific capacity and abundant resource.H...Silicon suboxide(SiO_(x),0<x<2)is recognized as one of the next-generation anode materials for high-energy-density lithium ion batteries(LIBs)due to its high theoretical specific capacity and abundant resource.However,the severe mechanical instability arising from large volume variation upon charge/discharge cycles frustrates its electrochemical performance.Here we propose a well-designed sandwich-like structure with sandwiched SiO_(x) nanoparticles between graphene sheets and amorphous carbon-coating layer so as to improve the structural stability of SiO_(x) anode materials during cycling.Graphene sheets and carbon layer together construct a three-dimensional conductive network around SiO_(x) particles,which not only improves the electrode reactions kinetics,but also homogenizes local current density and thus volume variation on SiO_(x) surface.Moreover,Si-O-C bonds between SiO_(x) and graphene endow the strong particle adhesion on graphene sheets,which prevents SiO_(x) peeling from graphene sheets.Owing to the synergetic effects of the structural advantages,the C/SiO_(x)@graphene material exhib-its an excellent cyclic performance such as 890 mAh/g at 0.1 C rate and 73.7%capacity retention after 100 cycles.In addition,it also delivers superior rate capability with a capacity recovery of 886 mAh/g(93.7%recovery rate)after 35 cycles of ascending steps at current range of 0.1-5 C and finally back to 0.1 C.This study provides a novel strategy to improve the structural stability of high-capacity anode materials for lithium/sodium ion batteries.展开更多
Segmentation of layers in retinal images obtained by optical coherence tomography(OCT)has become an important clinical tool to diagnose ophthalmic diseases.However,due to the sus-ceptibility to speckle noise and shado...Segmentation of layers in retinal images obtained by optical coherence tomography(OCT)has become an important clinical tool to diagnose ophthalmic diseases.However,due to the sus-ceptibility to speckle noise and shadow of blood vessels etc.,the layer segmentation technology based on a single image still fail to reach a satisfactory level.We propose a combination method of structure interpolation and lateral mean filtering(SI-LMF)to improve the signal-to-noise ratio based on one retinal image.Before performing one-dimensional lateral mean filtering to remove noise,structure interpolation was operated to eliminate thickness fluctuations.Then,we used boundary growth method to identify boundaries.Compared with existing segmentations,the method proposed in this paper requires less data and avoids the influence of microsaccade.The automatic segmentation method was verified on the spectral domain OCT volume images obtained from four normal objects,which successfully identified the boundaries of 10 physio-logical layers,consistent with the results based on the manual determination.展开更多
Silicon suboxide(SiOx)is considered to be one of the most promising materials for next-generation anode due to its high energy density.For its preparation,the wet-chemistry method is a cost-effective and readily scala...Silicon suboxide(SiOx)is considered to be one of the most promising materials for next-generation anode due to its high energy density.For its preparation,the wet-chemistry method is a cost-effective and readily scalable route,while the so-derived SiOx usually shows lower capacity compared with that prepared by high temperature-vacuum evaporation route.Herein,we present an elaborate particle structure design to realize the wet-chemistry preparation of a high-performance SiOx/C nanocomposite.Dandelion-like highly porous SiOx particle coated with conformal carbon layer is designed and prepared.The highly-porous SiOx skeleton provides plenty specific surface for intimate contact with carbon layer to allow a deep reduction of SiOx to a low O/Si ratio at relatively low temperature(700℃),enabling a high specific capacity.The abundant mesoscale voids effectively accommodate the volume variation of SiOx skeleton,ensuring the high structural stability of SiOx@C during lithiation/delithiation process.Meanwhile,the three-dimensional(3D)conformal carbon layer provides a fast electron/ion transportation,allowing an enhanced electrodereaction kinetics.Owing to the optimized O/Si ratio and well-engineered structure,the prepared SiOx@C electrode delivers an ultra-high capacity(1,115.8 mAh·g^-1 at 0.1 A·g^-1 after 200 cycles)and ultra-long lifespan(635 mAh·g^-1 at 2 A·g^-l after 1,000 cycles).To the best of our knowledge,the achieved combination of ultra-high specific capacity and ultra-long cycling life is unprecedented.展开更多
High nitrous oxide(N2O) emissions during freeze-thawing period(FTP) have been observed in many different ecosystems. However, the knowledge about the dynamic of soil N_2O emissions and its main driving mechanism durin...High nitrous oxide(N2O) emissions during freeze-thawing period(FTP) have been observed in many different ecosystems. However, the knowledge about the dynamic of soil N_2O emissions and its main driving mechanism during the freeze-thawing processes in grassland ecosystem is still limited. An in-situ experiment was conducted during the FTP on the sites with 0 and 15% surplus of the average rainfall and two levels of N addition(0,10 g N/(m^2·year)) during growing season(marked as W0N0, W15N0, W0N10, W15N10, respectively) to explore the effects of water and N background on soil N_2O emissions during FTPs and the relationship between soil N_2O emissions and environmental factors. The results indicated that water and N treatments conducted during growing season did not show significant effect on the N_2O effluxes of FTP, but the soil mineral N contents of W0N10 treatment were significantly higher than those of W0N0, W15N0, W15N10treatments(p < 0.05). The soil PLFA concentrations of microbial groups monitored during 2015 spring freeze-thawing period(2015S-FTP) were lower than those during winter freeze-thawing period of 2014(2014W-FTP), while cumulative soil N_2O emissions of 2015S-FTP were higher than those of 2014W-FTP. The correlations between soil N_2O effluxes and most of the measured environmental factors were insignificant, multiple stepwise regression analysis indicated that the soil temperature, soil NH_4^+-N content and air temperature were the major environmental factors which significantly influenced the N_2O effluxes during 2014W-FTP, and air temperature and soil water content were the significant influencing factors during 2015S-FTP.展开更多
The compositions of daughter mineral of melt inclusion in beryls, which are from pegmatites of Keketuhai in Xinjiang and Mufushan in Hunan, have been analyzed by electronic probe. Ten kinds of mineral, such as beryl, ...The compositions of daughter mineral of melt inclusion in beryls, which are from pegmatites of Keketuhai in Xinjiang and Mufushan in Hunan, have been analyzed by electronic probe. Ten kinds of mineral, such as beryl, zinc-spinel, mica, quartz, magnetite, etc., which consist of different mineral associations have been identified. The zinc-spinel existing in two dif-展开更多
Inspired by real biological neural models,Spiking Neural Networks(SNNs)process information with discrete spikes and show great potential for building low-power neural network systems.This paper proposes a hardware imp...Inspired by real biological neural models,Spiking Neural Networks(SNNs)process information with discrete spikes and show great potential for building low-power neural network systems.This paper proposes a hardware implementation of SNN based on Field-Programmable Gate Arrays(FPGA).It features a hybrid updating algorithm,which combines the advantages of existing algorithms to simplify hardware design and improve performance.The proposed design supports up to 16384 neurons and 16.8 million synapses but requires minimal hardware resources and archieves a very low power consumption of 0.477 W.A test platform is built based on the proposed design using a Xilinx FPGA evaluation board,upon which we deploy a classification task on the MNIST dataset.The evaluation results show an accuracy of 97.06%and a frame rate of 161 frames per second.展开更多
基金supported by the Interdisciplinary Research Project for Young Teachers of USTB (Fundamental Research Funds for the Central Universities) (No.FRFIDRY-21-023)the Beijing Natural Science Foundation (Nos.2194079 and 2222062)the National Natural Science Foundation of China (Nos.52074023 and 52102205)。
文摘Na_(3)V_(2)(PO_(4))_(2)O_(2)F(NVPOF)has received considerable interest as a promising cathode material for sodium-ion batteries because of its high working voltage and good structural/thermal stability.However,the sluggish electrode reaction resulting from its low intrinsic electronic conductivity significantly restricts its electrochemical performance and thus its practical application.Herein,Nb-doped Na_(3)V_(2-x)Nb_(x)(PO_(4))_(2)O_(2)F/graphene(rGO)composites(x=0,0.05,0.1)were prepared using a solvothermal method followed by calcination.Compared to the un-doped NVPOF/r GO,doping V-site with high-valence Nb element(Nb^(5+))(Na_(3)V_(1.95)Nb_(0.05)(PO_(4))_(2)O_(2)F/r GO(NVN05POF/rGO))can result in the generated V4^(+)/V3^(+)mixed-valence,ensuring the lower bandgap and thus the increased intrinsic electronic conductivity.Besides,the expanded lattice space favors the Na^(+)migration.With the structure feature where NVN05POF particles are attached to the rGO sheets,the electrode reaction kinetics is further accelerated owing to the well-constructed electron conductive network.As a consequence,the as-prepared NVN05POF/r GO sample exhibits a high specific capacity of~72 m Ah·g^(-1)at 10C(capacity retention of 65.2%(vs.0.5C))and excellent long-term cycling stability with the capacity fading rate of~0.099%per cycle in 500 cycles at 5C.
基金financially supported by the National Natural Science Foundation of China (Nos. 52102205 and U1637202)the Fundamental Research Funds for the Central Universities (No. FRF-TP-20-048A1)
文摘Silicon suboxide(SiO_(x),0<x<2)is recognized as one of the next-generation anode materials for high-energy-density lithium ion batteries(LIBs)due to its high theoretical specific capacity and abundant resource.However,the severe mechanical instability arising from large volume variation upon charge/discharge cycles frustrates its electrochemical performance.Here we propose a well-designed sandwich-like structure with sandwiched SiO_(x) nanoparticles between graphene sheets and amorphous carbon-coating layer so as to improve the structural stability of SiO_(x) anode materials during cycling.Graphene sheets and carbon layer together construct a three-dimensional conductive network around SiO_(x) particles,which not only improves the electrode reactions kinetics,but also homogenizes local current density and thus volume variation on SiO_(x) surface.Moreover,Si-O-C bonds between SiO_(x) and graphene endow the strong particle adhesion on graphene sheets,which prevents SiO_(x) peeling from graphene sheets.Owing to the synergetic effects of the structural advantages,the C/SiO_(x)@graphene material exhib-its an excellent cyclic performance such as 890 mAh/g at 0.1 C rate and 73.7%capacity retention after 100 cycles.In addition,it also delivers superior rate capability with a capacity recovery of 886 mAh/g(93.7%recovery rate)after 35 cycles of ascending steps at current range of 0.1-5 C and finally back to 0.1 C.This study provides a novel strategy to improve the structural stability of high-capacity anode materials for lithium/sodium ion batteries.
基金This work was supported in part by National Natural Science Foundation of China(61771119 and 61901100)Hebei Provincial Natural Science Foundation of China(H2018501087 and H2019501010)Fundamental Research Funds for the Central Universities(N182304008).
文摘Segmentation of layers in retinal images obtained by optical coherence tomography(OCT)has become an important clinical tool to diagnose ophthalmic diseases.However,due to the sus-ceptibility to speckle noise and shadow of blood vessels etc.,the layer segmentation technology based on a single image still fail to reach a satisfactory level.We propose a combination method of structure interpolation and lateral mean filtering(SI-LMF)to improve the signal-to-noise ratio based on one retinal image.Before performing one-dimensional lateral mean filtering to remove noise,structure interpolation was operated to eliminate thickness fluctuations.Then,we used boundary growth method to identify boundaries.Compared with existing segmentations,the method proposed in this paper requires less data and avoids the influence of microsaccade.The automatic segmentation method was verified on the spectral domain OCT volume images obtained from four normal objects,which successfully identified the boundaries of 10 physio-logical layers,consistent with the results based on the manual determination.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.U1637202 and 51634003)the National Key R&D Program of China(No.2018YFB0905600)Beijing Municipal Education Commission-Natural Science Foundation Joint Key Project(No.KZ201910005003).
文摘Silicon suboxide(SiOx)is considered to be one of the most promising materials for next-generation anode due to its high energy density.For its preparation,the wet-chemistry method is a cost-effective and readily scalable route,while the so-derived SiOx usually shows lower capacity compared with that prepared by high temperature-vacuum evaporation route.Herein,we present an elaborate particle structure design to realize the wet-chemistry preparation of a high-performance SiOx/C nanocomposite.Dandelion-like highly porous SiOx particle coated with conformal carbon layer is designed and prepared.The highly-porous SiOx skeleton provides plenty specific surface for intimate contact with carbon layer to allow a deep reduction of SiOx to a low O/Si ratio at relatively low temperature(700℃),enabling a high specific capacity.The abundant mesoscale voids effectively accommodate the volume variation of SiOx skeleton,ensuring the high structural stability of SiOx@C during lithiation/delithiation process.Meanwhile,the three-dimensional(3D)conformal carbon layer provides a fast electron/ion transportation,allowing an enhanced electrodereaction kinetics.Owing to the optimized O/Si ratio and well-engineered structure,the prepared SiOx@C electrode delivers an ultra-high capacity(1,115.8 mAh·g^-1 at 0.1 A·g^-1 after 200 cycles)and ultra-long lifespan(635 mAh·g^-1 at 2 A·g^-l after 1,000 cycles).To the best of our knowledge,the achieved combination of ultra-high specific capacity and ultra-long cycling life is unprecedented.
基金financially supported by the National Natural Science Foundation of China(22005149,21975129,and 22172077)the Natural Science Foundation of Jiangsu Province(BK20200777 and BK20211573)+1 种基金the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province,China(20KJB430034)the Science Fund for Distinguished Young Scholars,Nanjing Forestry University(JC2019002)。
基金supported by the National Natural Science Foundation of China(Nos.41373084,41330528,and 41203054)
文摘High nitrous oxide(N2O) emissions during freeze-thawing period(FTP) have been observed in many different ecosystems. However, the knowledge about the dynamic of soil N_2O emissions and its main driving mechanism during the freeze-thawing processes in grassland ecosystem is still limited. An in-situ experiment was conducted during the FTP on the sites with 0 and 15% surplus of the average rainfall and two levels of N addition(0,10 g N/(m^2·year)) during growing season(marked as W0N0, W15N0, W0N10, W15N10, respectively) to explore the effects of water and N background on soil N_2O emissions during FTPs and the relationship between soil N_2O emissions and environmental factors. The results indicated that water and N treatments conducted during growing season did not show significant effect on the N_2O effluxes of FTP, but the soil mineral N contents of W0N10 treatment were significantly higher than those of W0N0, W15N0, W15N10treatments(p < 0.05). The soil PLFA concentrations of microbial groups monitored during 2015 spring freeze-thawing period(2015S-FTP) were lower than those during winter freeze-thawing period of 2014(2014W-FTP), while cumulative soil N_2O emissions of 2015S-FTP were higher than those of 2014W-FTP. The correlations between soil N_2O effluxes and most of the measured environmental factors were insignificant, multiple stepwise regression analysis indicated that the soil temperature, soil NH_4^+-N content and air temperature were the major environmental factors which significantly influenced the N_2O effluxes during 2014W-FTP, and air temperature and soil water content were the significant influencing factors during 2015S-FTP.
文摘The compositions of daughter mineral of melt inclusion in beryls, which are from pegmatites of Keketuhai in Xinjiang and Mufushan in Hunan, have been analyzed by electronic probe. Ten kinds of mineral, such as beryl, zinc-spinel, mica, quartz, magnetite, etc., which consist of different mineral associations have been identified. The zinc-spinel existing in two dif-
基金supported in part by the Beijing Innovation Center for Future Chip,Tsinghua Universityin part by the Science and Technology Innovation Special Zone project,Chinain part by the Tsinghua University Initiative Scientific Research Program(No.2018Z05JDX005).
文摘Inspired by real biological neural models,Spiking Neural Networks(SNNs)process information with discrete spikes and show great potential for building low-power neural network systems.This paper proposes a hardware implementation of SNN based on Field-Programmable Gate Arrays(FPGA).It features a hybrid updating algorithm,which combines the advantages of existing algorithms to simplify hardware design and improve performance.The proposed design supports up to 16384 neurons and 16.8 million synapses but requires minimal hardware resources and archieves a very low power consumption of 0.477 W.A test platform is built based on the proposed design using a Xilinx FPGA evaluation board,upon which we deploy a classification task on the MNIST dataset.The evaluation results show an accuracy of 97.06%and a frame rate of 161 frames per second.