The ultra-fast cooling technology of large section bars and the microstrueture for different cooling patterns were studied by optical microscope, transmission electron microscope and energy spectrometer. The results i...The ultra-fast cooling technology of large section bars and the microstrueture for different cooling patterns were studied by optical microscope, transmission electron microscope and energy spectrometer. The results indicated that the large section bars were passed through the zone of secondary carbide precipitation quickly by ultra-fast cooling technology （UFC） at instantaneous cooling rate of about 200 ℃/s and the finishing cooling temperature was higher than Ms. The lamellar spacing of pearlite decreased and the microhardness increased with decreasing the rereddening temperature. The precipitation of network carbide was restrained when re-reddening temperature was 690 ℃. And fine laminated pearlite was obtained through transformation of pseudopearlition that induced the reduction of the diameter of pearlite grain and refinement of the lamellar spacing of pearlite, so ideal microstructures of promoting spheroidizing annealing were obtained.展开更多
Smart fire alarm sensor(FAS)materials with mechanically robust,excellent flame retardancy as well as ultra-sensitive temperature-responsive capability are highly attractive platforms for fire safety application.Howeve...Smart fire alarm sensor(FAS)materials with mechanically robust,excellent flame retardancy as well as ultra-sensitive temperature-responsive capability are highly attractive platforms for fire safety application.However,most reported FAS materials can hardly provide sensitive,continuous and reliable alarm signal output due to their undesirable temperature-responsive,flame-resistant and mechanical performances.To overcome these hurdles,herein,we utilize the multi-amino molecule,named HCPA,that can serve as triple-roles including cross-linker,fire retardant and reducing agent for decorating graphene oxide(GO)sheets and obtaining the GO/HCPA hybrid networks.Benefiting from the formation of multi-interactions in hybrid network,the optimized GO/HCPA network exhibits significant increment in mechanical strength,e.g.,tensile strength and toughness increase of~2.3and~5.7 times,respectively,compared to the control one.More importantly,based on P and N doping and promoting thermal reduction effect on GO network,the excellent flame retardancy(withstanding~1200℃flame attack),ultra-fast fire alarm response time(~0.6 s)and ultra-long alarming period(>600 s)are obtained,representing the best comprehensive performance of GO-based FAS counterparts.Furthermore,based on GO/HCPA network,the fireproof coating is constructed and applied in polymer foam and exhibited exceptional fire shielding performance.This work provides a new idea for designing and fabricating desirable FAS materials and fireproof coatings.展开更多
Temperature deviation between surface and the center of hot rolled strip is formed during ultra-fast cooling （UFC）. Surface temperature would rise when temperature deviation goes up to an extent, and strip re-redden...Temperature deviation between surface and the center of hot rolled strip is formed during ultra-fast cooling （UFC）. Surface temperature would rise when temperature deviation goes up to an extent, and strip re-reddening phenomenon will appear. Strip re-reddening affects the stability of strip microstructure, property and temperature control precision. Thus, it is necessary to conduct research on re-reddening temperature changing law to improve strip property and temperature control precision. Strip temperature trends for various strip thicknesses and ultra-fast cooling rates were obtained by numerical calculation method. Re-reddening temperature, temperature deviation between surface and center, and boundary layer position changing law were obtained. By comparison, some conclusions were obtained： UFC re-reddening temperature and laminar cooling （LC） re-reddening temperature were linear to ultra-fast cooling rate respectively. Ultra-fast cooling rate affected UFC re-reddening temperature greatly, but it had little effect on LC re-reddening temperature. Equations which were used to calculate UFC re-reddening temperature, LC re-reddening temperature and maximum temperature deviation were obtained. The position of boundary layer stayed in 1/4 strip thickness.展开更多
The fluid flow characteristics of the single bunch inclined jet impingement were investigated with different jet flow velocities,nozzle diameters,jet angles and jet-to-target distances for ultra-fast cooling technolog...The fluid flow characteristics of the single bunch inclined jet impingement were investigated with different jet flow velocities,nozzle diameters,jet angles and jet-to-target distances for ultra-fast cooling technology.The results show that the peak pressure varying significantly from nearly 0.5 to above 13.4 kPa locates at the stagnation point with different jet diameters,and the radius of impact pressure affected zone is small promoted from 46 to 81 mm in transverse direction,and 50 to 91 mm in longitude direction when the jet flow velocity changes from 5 to 20 m/s.However,the fluid flow velocity is relatively smaller near the stagnation point,and increases gradually along the radius outwards,then declines.There is an obvious anisotropic characteristic that the flow velocity component along the jet direction is about twice of the contrary one where the jet anlge is 60°,jet diameter is 5 mm,jet length is 8 mm and jet height is 50 mm.展开更多
New generation thermo-mechanical control process（TMCP） based on ultra-fast cooling is being widely adopted in plate mill to product high-performance steel material at low cost. Ultra-fast cooling system is complex b...New generation thermo-mechanical control process（TMCP） based on ultra-fast cooling is being widely adopted in plate mill to product high-performance steel material at low cost. Ultra-fast cooling system is complex because of optimizing the temperature control error generated by heat transfer mathematical model and process parameters. In order to simplify the system and improve the temperature control precision in ultra-fast cooling process, several existing models of case-based reasoning（CBR） model are reviewed. Combining with ultra-fast cooling process, a developed R5 CBR model is proposed, which mainly improves the case representation, similarity relation and retrieval module. Certainty factor is defined in semantics memory unit of plate case which provides not only internal data reliability but also product performance reliability. Similarity relation is improved by defined power index similarity membership function. Retrieval process is simplified and retrieval efficiency is improved apparently by windmill retrieval algorithm. The proposed CBR model is used for predicting the case of cooling strategy and its capability is superior to traditional process model. In order to perform comprehensive investigations on ultra-fast cooling process, different steel plates are considered for the experiment. The validation experiment and industrial production of proposed CBR model are carried out, which demonstrated that finish cooling temperature（FCT） error is controlled within±25℃ and quality rate of product is more than 97%. The proposed CBR model can simplify ultra-fast cooling system and give quality performance for steel product.展开更多
Thermal conductivity is an important material parameter of silicon when studying the performance and reliability of devices or for guiding circuit design when considering heat dissipation, especially when the self-hea...Thermal conductivity is an important material parameter of silicon when studying the performance and reliability of devices or for guiding circuit design when considering heat dissipation, especially when the self-heating effect becomes prominent in ultra-scaled MOSFETs.The cross-plane thermal conductivity of a thin silicon film is lacking due to the difficulty in sensing high thermal conductivity in the vertical direction.In this paper, a feasible method that utilizes an ultra-fast electrical pulse within 20 μs combined with the hot strip technique is adopted.To the best of our knowledge, this is the first work that shows how to extract the cross-plane thermal conductivity of sub-50 nm(30 nm, 17 nm, and 10 nm)silicon films on buried oxide.The ratio of the extracted cross-plane thermal conductivity of the silicon films over the bulk value is only about 6.9%, 4.3%, and 3.8% at 300 K, respectively.As the thickness of the films is smaller than the phonon mean free path, the classical heat transport theory fails to predict the heat dissipation in nanoscale transistors.Thus, in this study, a ballistic model, derived from the heat transport equation based on extended-irreversible-hydrodynamics(EIT), is used for further investigation, and the simulation results exhibit good consistence with the experimental data.The extracted effective thermal data could provide a good reference for precise device simulations and thermoelectric applications.展开更多
Ultra-fast x-ray-dynamic experimental subsystem is a facility which can provide femtosecond hard x-ray sources using a femtosecond laser interacting with plasmas. By utilizing these ultra-fast x-rays as a probe, combi...Ultra-fast x-ray-dynamic experimental subsystem is a facility which can provide femtosecond hard x-ray sources using a femtosecond laser interacting with plasmas. By utilizing these ultra-fast x-rays as a probe, combined with a naturally synchronized driver laser as a pump, we can perform dynamic studies on samples with a femtosecond time resolution. This subsystem with a four-dimensional ultra-high spatiotemporal resolution is a powerful tool for studies of the process of photosynthesis, Auger electron effects, lattice vibrations, etc. Compared with conventional x-ray sources based on accelerators, this table-top laser-driven x-ray source has significant advantages in terms of the source size, pulse duration, brightness, flexibility, and economy. It is an effective supplement to the synchrotron light source in the ultrafast detection regime.展开更多
While we process observational data of the Flares 22, two rare phenomena of microwave ultra fast absorption (MUFA) are found for the first time. They occurred at 3 67 GHz and 4 00 GHz in the atmospheric layers above b...While we process observational data of the Flares 22, two rare phenomena of microwave ultra fast absorption (MUFA) are found for the first time. They occurred at 3 67 GHz and 4 00 GHz in the atmospheric layers above both active regions of NOAA/USAF 4808 and 5060 in the interval 05 h50 m17 s～05 h50 m25 s UT on May 19, 1987 and 07 h38 m50 s～07 h38 m58 s UT on June 29, 1988, respectively. These absorption phenomena were observed with Phoenix Ⅱ Micowave Spectrometer at three frequencies (1 42, 2 84 and 3 67 GHz) and (1 42, 2 84 and 4 00 GHz) at Yunnan observatory. Spike emissions appeared at both 2 84 GHz and 1 42 GHz. The notable observational characteristics of both absorption phenomena are given. A possible absorption mechanism of MUFA is discussed.展开更多
Organic cathode materials hold great promise for rechargeable batteries due to their high theoretical capacity, sustainable resources, and low carbon footprint, yet suffer from low conductivity and high solubility in ...Organic cathode materials hold great promise for rechargeable batteries due to their high theoretical capacity, sustainable resources, and low carbon footprint, yet suffer from low conductivity and high solubility in liquid electrolytes, which result in inferior kinetics and poor cycling stability. Herein, we rationally design and synthesize a new conjugated carbonyl polymer(PTO-AQ) cathode with a unique donor-acceptor structure. The polymerization can effectively eliminate the dissolution of organic molecules, while the interlaced donor and acceptor units can endow the PTO-AQ polymer to serve as both donors and acceptors of electrons, thereby enhancing the electrical conductivity. Consequently, the PTO-AQ cathode exhibits high capacity,remarkable cycling stability, and high-rate performance in both Li and Na batteries. Notably, when paired with a Na-metal or hard carbon anode, the resulting Na batteries can stably operate for over 10,000 cycles with an extremely low-capacity decay rate(<0.5% per 100 cycles) and retain a high capacity of 66 m Ah g^(-1)at an ultra-high current density of 40 A g^(-1), representing a significant advancement in promoting organic batteries with long-cycling and ultra-fast charging.展开更多
Time-resolved MeV ultra-fast electron diffraction (UED) is a powerful tool for structure dynamics studies. In this paper, we present a design of a MeV UED facility based on a photocathode RF gun at Tsinghua University...Time-resolved MeV ultra-fast electron diffraction (UED) is a powerful tool for structure dynamics studies. In this paper, we present a design of a MeV UED facility based on a photocathode RF gun at Tsinghua University. Electron beam qualities are optimized with numerical simulations, indicating that resolutions of 250 fs and 0.01 , and bunch charge exceeding 105 electrons are expected with technically achievable machine parameters. Status of experiment preparation is also presented.展开更多
Gold nanocages （AuNcgs） are well-studied, hollow, metallic nanostructures that have fascinated researchers in the fields of nanotechnology, materials science, photoelectronics, biotechnology, and medical science for...Gold nanocages （AuNcgs） are well-studied, hollow, metallic nanostructures that have fascinated researchers in the fields of nanotechnology, materials science, photoelectronics, biotechnology, and medical science for the last decade. However, the time-consuming synthesis of AuNcgs has limited their widespread use in materials science and nano-biotechnology. A novel, ultra-fast, simple, and highly convenient method for the production of AuNcgs using microwave heating is demonstrated herein. This quick method of AuNcg synthesis requires mild laboratory conditions for large-scale production of AuNcgs. The microwave heating technique offers the advantage of precise mechanical control over the temperature and heating power, even for the shortest reaction period （i.e., seconds）. Microwave-synthesized AuNcgs were compared with conventionally synthesized AuNcgs. Structural maneuver studies employing the conventionally produced AuNcgs revealed the formation of screw dislocations and a shift in the lattice plane. Detailed characterization of the microwave-generated AuNcgs was performed using high resolution transmission electron microscopy （HRTEM）, scanning electron microscopy （SEM）, X-ray powder diffraction （XRD）, and spectroscopic techniques.展开更多
The rapid development of capacitors with high energy density and efficiency has been driven by advanced electronic systems and innovative pulsed power applications.In this study,we prepared Sr_(4.5−x)Ba_(x)Sm_(0.5)Zr_...The rapid development of capacitors with high energy density and efficiency has been driven by advanced electronic systems and innovative pulsed power applications.In this study,we prepared Sr_(4.5−x)Ba_(x)Sm_(0.5)Zr_(0.5)Nb_(9.5)O_(30)(x=2.5,3,3.5,4,4.5)dielectric ceramics,which exhibited structural distortion due to the co-occupation of Ba^(2+),Sr^(2+),and Sm^(3+)in the A-site and the partial substitution of Nb^(5+)by Zr^(4+)in the B-site.The ordered/disordered distribution due to these distortions thus generated polar nanoregions(PNRs)and induced a relaxation ferroelectric behavior,which was verified by the high-resolution transmission electron microscopy.Through the use of the Vogel–Fulcher and Maxwell–Boltzmann equations,we found that easy inversion and small dipole sizes are crucial for achieving high energy storage density and efficiency.The Sr_(4.5−x)Ba_(x)Sm_(0.5)Zr_(0.5)Nb_(9.5)O_(30)(x=3.5)dielectric ceramic displayed a ferroelectric/paraelectric transition near room temperature.Subsequent ferroelectric testing revealed large energy storage density(Wrec=4.31 J·cm^(−3))and high efficiency(η=93.8%)at 310 kV·cm−1.Furthermore,Sr_(4.5−x)Ba_(x)Sm_(0.5)Zr_(0.5)Nb_(9.5)O_(30)(x=4.5)exhibited higher breakdown field strength due to its large resistivity and small grain size.This led to energy storage density of approximately 5.3 J·cm^(−3)at 460 kV·cm^(−1).Additionally,Sr_(4.5−x)Ba_(x)Sm_(0.5)Zr_(0.5)Nb_(9.5)O_(30)(x=3.5)demonstrated current density(CD)of approximately 713.38 A·cm^(−2)and power density(PD)of approximately 87.51 MW·cm^(−3),with ultrafast discharge time of 34 ns and excellent discharge energy density(Wdis)of approximately 2.27 J·cm^(−3).Overall,this study presents a promising approach for developing dielectric ceramic materials that hold potential for applications in innovative pulsed power components.展开更多
Lead-free relaxor ceramics(1−x)K_(0.5)Na_(0.5)NbO_(3)−xBi(Mn_(0.5)Ni_(0.5))O_(3)((1−x)KNN-xBMN)with considerable charge-discharge characteristics and energy storage properties were prepared by a solid state method.Rem...Lead-free relaxor ceramics(1−x)K_(0.5)Na_(0.5)NbO_(3)−xBi(Mn_(0.5)Ni_(0.5))O_(3)((1−x)KNN-xBMN)with considerable charge-discharge characteristics and energy storage properties were prepared by a solid state method.Remarkable,a BMN doping level of 0.04,0.96KNN-0.04BMN ceramic obtained good energy storage performance with acceptable energy storage density Wrec of 1.826 J/cm^(3) and energy storage efficiencyηof 77.4%,as well as good frequency stability(1-500 Hz)and fatigue resistance(1-5000 cycles).Meanwhile,a satisfactory charge-discharge performance with power density PD~98.90 MW/cm^(3),discharge time t0.9<70 ns and temperature stability(30-180°C)was obtained in 0.96KNN-0.04BMN ceramic.The small grain size(~150 nm)and the high polarizability of Bi3+are directly related to its good energy storage capacity.This work proposes a feasible approach for lead-free KNN-based ceramics to achieve high-energy storage and ultra-fast charge-discharge performance as well as candidate materials for the application of advanced high-temperature pulse capacitors.展开更多
Neutral fragments of methane were performed using femetosecond laser at an intensity of 1013-14W/cm2. A new mechanism of neutral dissociation is proposed in this work. The methane molecule is excited to super-excited ...Neutral fragments of methane were performed using femetosecond laser at an intensity of 1013-14W/cm2. A new mechanism of neutral dissociation is proposed in this work. The methane molecule is excited to super-excited states,in which it would dissociate into neutral fragments. We made Morse type potential energy surfaces for the super-excited molecules. Furthermore,we investigated the dissociation dy-namics of the super-excited states by using quasi-classical trajectory (QCT) method. The results thus interpret the neutral dissociation of the methane molecule in the ultra-fast laser pulse.展开更多
基金Sponsored by National Natural Science Foundation of China(50334010)
文摘The ultra-fast cooling technology of large section bars and the microstrueture for different cooling patterns were studied by optical microscope, transmission electron microscope and energy spectrometer. The results indicated that the large section bars were passed through the zone of secondary carbide precipitation quickly by ultra-fast cooling technology （UFC） at instantaneous cooling rate of about 200 ℃/s and the finishing cooling temperature was higher than Ms. The lamellar spacing of pearlite decreased and the microhardness increased with decreasing the rereddening temperature. The precipitation of network carbide was restrained when re-reddening temperature was 690 ℃. And fine laminated pearlite was obtained through transformation of pseudopearlition that induced the reduction of the diameter of pearlite grain and refinement of the lamellar spacing of pearlite, so ideal microstructures of promoting spheroidizing annealing were obtained.
基金The research work was financially supported by the Australian Research Council(Nos.DE190101176,FT190100188,DP190102992,IC170100032)the National Natural Science Foundation of China(51973047)+2 种基金the Project for the Science and Technology Program of Hangzhou(20201203B136,20201203B134)the International Collaboration Programs of Guangdong Province(2020A0505100010)Open access funding provided by Shanghai Jiao Tong University
文摘Smart fire alarm sensor(FAS)materials with mechanically robust,excellent flame retardancy as well as ultra-sensitive temperature-responsive capability are highly attractive platforms for fire safety application.However,most reported FAS materials can hardly provide sensitive,continuous and reliable alarm signal output due to their undesirable temperature-responsive,flame-resistant and mechanical performances.To overcome these hurdles,herein,we utilize the multi-amino molecule,named HCPA,that can serve as triple-roles including cross-linker,fire retardant and reducing agent for decorating graphene oxide(GO)sheets and obtaining the GO/HCPA hybrid networks.Benefiting from the formation of multi-interactions in hybrid network,the optimized GO/HCPA network exhibits significant increment in mechanical strength,e.g.,tensile strength and toughness increase of~2.3and~5.7 times,respectively,compared to the control one.More importantly,based on P and N doping and promoting thermal reduction effect on GO network,the excellent flame retardancy(withstanding~1200℃flame attack),ultra-fast fire alarm response time(~0.6 s)and ultra-long alarming period(>600 s)are obtained,representing the best comprehensive performance of GO-based FAS counterparts.Furthermore,based on GO/HCPA network,the fireproof coating is constructed and applied in polymer foam and exhibited exceptional fire shielding performance.This work provides a new idea for designing and fabricating desirable FAS materials and fireproof coatings.
基金Sponsored by State"1025"Science and Technology Support Projects of China(2012BAF04B01)
文摘Temperature deviation between surface and the center of hot rolled strip is formed during ultra-fast cooling （UFC）. Surface temperature would rise when temperature deviation goes up to an extent, and strip re-reddening phenomenon will appear. Strip re-reddening affects the stability of strip microstructure, property and temperature control precision. Thus, it is necessary to conduct research on re-reddening temperature changing law to improve strip property and temperature control precision. Strip temperature trends for various strip thicknesses and ultra-fast cooling rates were obtained by numerical calculation method. Re-reddening temperature, temperature deviation between surface and center, and boundary layer position changing law were obtained. By comparison, some conclusions were obtained： UFC re-reddening temperature and laminar cooling （LC） re-reddening temperature were linear to ultra-fast cooling rate respectively. Ultra-fast cooling rate affected UFC re-reddening temperature greatly, but it had little effect on LC re-reddening temperature. Equations which were used to calculate UFC re-reddening temperature, LC re-reddening temperature and maximum temperature deviation were obtained. The position of boundary layer stayed in 1/4 strip thickness.
基金Project(2010CB630800)supported by the National Basic Research Program of ChinaProject(N100307003)supported by the Fundamental Research Funds for the Central Universities,China
文摘The fluid flow characteristics of the single bunch inclined jet impingement were investigated with different jet flow velocities,nozzle diameters,jet angles and jet-to-target distances for ultra-fast cooling technology.The results show that the peak pressure varying significantly from nearly 0.5 to above 13.4 kPa locates at the stagnation point with different jet diameters,and the radius of impact pressure affected zone is small promoted from 46 to 81 mm in transverse direction,and 50 to 91 mm in longitude direction when the jet flow velocity changes from 5 to 20 m/s.However,the fluid flow velocity is relatively smaller near the stagnation point,and increases gradually along the radius outwards,then declines.There is an obvious anisotropic characteristic that the flow velocity component along the jet direction is about twice of the contrary one where the jet anlge is 60°,jet diameter is 5 mm,jet length is 8 mm and jet height is 50 mm.
基金Supported by National Basic Research Program of China (973 Program,Grant No.2010CB630801)
文摘New generation thermo-mechanical control process（TMCP） based on ultra-fast cooling is being widely adopted in plate mill to product high-performance steel material at low cost. Ultra-fast cooling system is complex because of optimizing the temperature control error generated by heat transfer mathematical model and process parameters. In order to simplify the system and improve the temperature control precision in ultra-fast cooling process, several existing models of case-based reasoning（CBR） model are reviewed. Combining with ultra-fast cooling process, a developed R5 CBR model is proposed, which mainly improves the case representation, similarity relation and retrieval module. Certainty factor is defined in semantics memory unit of plate case which provides not only internal data reliability but also product performance reliability. Similarity relation is improved by defined power index similarity membership function. Retrieval process is simplified and retrieval efficiency is improved apparently by windmill retrieval algorithm. The proposed CBR model is used for predicting the case of cooling strategy and its capability is superior to traditional process model. In order to perform comprehensive investigations on ultra-fast cooling process, different steel plates are considered for the experiment. The validation experiment and industrial production of proposed CBR model are carried out, which demonstrated that finish cooling temperature（FCT） error is controlled within±25℃ and quality rate of product is more than 97%. The proposed CBR model can simplify ultra-fast cooling system and give quality performance for steel product.
基金Project supported by the Zhejiang Provincial Natural Science Foundation of China(Grant No.LZ19F040001)the National Natural Science Foundation of China(Grant No.61473287)the NSFC–Zhejiang Joint Fund for the Integration of Industrialization Informatization,China(Grant No.U1609213)
文摘Thermal conductivity is an important material parameter of silicon when studying the performance and reliability of devices or for guiding circuit design when considering heat dissipation, especially when the self-heating effect becomes prominent in ultra-scaled MOSFETs.The cross-plane thermal conductivity of a thin silicon film is lacking due to the difficulty in sensing high thermal conductivity in the vertical direction.In this paper, a feasible method that utilizes an ultra-fast electrical pulse within 20 μs combined with the hot strip technique is adopted.To the best of our knowledge, this is the first work that shows how to extract the cross-plane thermal conductivity of sub-50 nm(30 nm, 17 nm, and 10 nm)silicon films on buried oxide.The ratio of the extracted cross-plane thermal conductivity of the silicon films over the bulk value is only about 6.9%, 4.3%, and 3.8% at 300 K, respectively.As the thickness of the films is smaller than the phonon mean free path, the classical heat transport theory fails to predict the heat dissipation in nanoscale transistors.Thus, in this study, a ballistic model, derived from the heat transport equation based on extended-irreversible-hydrodynamics(EIT), is used for further investigation, and the simulation results exhibit good consistence with the experimental data.The extracted effective thermal data could provide a good reference for precise device simulations and thermoelectric applications.
基金Project supported by the National Major Science and Technology Infrastructure Construction Project "Synergetic Extreme Condition User Facility",China
文摘Ultra-fast x-ray-dynamic experimental subsystem is a facility which can provide femtosecond hard x-ray sources using a femtosecond laser interacting with plasmas. By utilizing these ultra-fast x-rays as a probe, combined with a naturally synchronized driver laser as a pump, we can perform dynamic studies on samples with a femtosecond time resolution. This subsystem with a four-dimensional ultra-high spatiotemporal resolution is a powerful tool for studies of the process of photosynthesis, Auger electron effects, lattice vibrations, etc. Compared with conventional x-ray sources based on accelerators, this table-top laser-driven x-ray source has significant advantages in terms of the source size, pulse duration, brightness, flexibility, and economy. It is an effective supplement to the synchrotron light source in the ultrafast detection regime.
文摘While we process observational data of the Flares 22, two rare phenomena of microwave ultra fast absorption (MUFA) are found for the first time. They occurred at 3 67 GHz and 4 00 GHz in the atmospheric layers above both active regions of NOAA/USAF 4808 and 5060 in the interval 05 h50 m17 s～05 h50 m25 s UT on May 19, 1987 and 07 h38 m50 s～07 h38 m58 s UT on June 29, 1988, respectively. These absorption phenomena were observed with Phoenix Ⅱ Micowave Spectrometer at three frequencies (1 42, 2 84 and 3 67 GHz) and (1 42, 2 84 and 4 00 GHz) at Yunnan observatory. Spike emissions appeared at both 2 84 GHz and 1 42 GHz. The notable observational characteristics of both absorption phenomena are given. A possible absorption mechanism of MUFA is discussed.
基金supported by the National Natural Science Foundation of China (22005108)the Natural Science Foundation of Guangdong Province (2022B1515020005, 2023B1515130004, 2023A1515012032)+1 种基金the Guangzhou Science and Technology Foundation (2024A04J4192)the Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education) of Nankai University。
文摘Organic cathode materials hold great promise for rechargeable batteries due to their high theoretical capacity, sustainable resources, and low carbon footprint, yet suffer from low conductivity and high solubility in liquid electrolytes, which result in inferior kinetics and poor cycling stability. Herein, we rationally design and synthesize a new conjugated carbonyl polymer(PTO-AQ) cathode with a unique donor-acceptor structure. The polymerization can effectively eliminate the dissolution of organic molecules, while the interlaced donor and acceptor units can endow the PTO-AQ polymer to serve as both donors and acceptors of electrons, thereby enhancing the electrical conductivity. Consequently, the PTO-AQ cathode exhibits high capacity,remarkable cycling stability, and high-rate performance in both Li and Na batteries. Notably, when paired with a Na-metal or hard carbon anode, the resulting Na batteries can stably operate for over 10,000 cycles with an extremely low-capacity decay rate(<0.5% per 100 cycles) and retain a high capacity of 66 m Ah g^(-1)at an ultra-high current density of 40 A g^(-1), representing a significant advancement in promoting organic batteries with long-cycling and ultra-fast charging.
基金Supported by NSFC (10735050,10875070)National Basic Research Program of China (973 Program)(2007CB815102)
文摘Time-resolved MeV ultra-fast electron diffraction (UED) is a powerful tool for structure dynamics studies. In this paper, we present a design of a MeV UED facility based on a photocathode RF gun at Tsinghua University. Electron beam qualities are optimized with numerical simulations, indicating that resolutions of 250 fs and 0.01 , and bunch charge exceeding 105 electrons are expected with technically achievable machine parameters. Status of experiment preparation is also presented.
文摘Gold nanocages （AuNcgs） are well-studied, hollow, metallic nanostructures that have fascinated researchers in the fields of nanotechnology, materials science, photoelectronics, biotechnology, and medical science for the last decade. However, the time-consuming synthesis of AuNcgs has limited their widespread use in materials science and nano-biotechnology. A novel, ultra-fast, simple, and highly convenient method for the production of AuNcgs using microwave heating is demonstrated herein. This quick method of AuNcg synthesis requires mild laboratory conditions for large-scale production of AuNcgs. The microwave heating technique offers the advantage of precise mechanical control over the temperature and heating power, even for the shortest reaction period （i.e., seconds）. Microwave-synthesized AuNcgs were compared with conventionally synthesized AuNcgs. Structural maneuver studies employing the conventionally produced AuNcgs revealed the formation of screw dislocations and a shift in the lattice plane. Detailed characterization of the microwave-generated AuNcgs was performed using high resolution transmission electron microscopy （HRTEM）, scanning electron microscopy （SEM）, X-ray powder diffraction （XRD）, and spectroscopic techniques.
基金the National Natural Science Foundation of China(No.12164012)the Science and Technology Major Project of Guangxi(No.AA21077012)for financial support.
文摘The rapid development of capacitors with high energy density and efficiency has been driven by advanced electronic systems and innovative pulsed power applications.In this study,we prepared Sr_(4.5−x)Ba_(x)Sm_(0.5)Zr_(0.5)Nb_(9.5)O_(30)(x=2.5,3,3.5,4,4.5)dielectric ceramics,which exhibited structural distortion due to the co-occupation of Ba^(2+),Sr^(2+),and Sm^(3+)in the A-site and the partial substitution of Nb^(5+)by Zr^(4+)in the B-site.The ordered/disordered distribution due to these distortions thus generated polar nanoregions(PNRs)and induced a relaxation ferroelectric behavior,which was verified by the high-resolution transmission electron microscopy.Through the use of the Vogel–Fulcher and Maxwell–Boltzmann equations,we found that easy inversion and small dipole sizes are crucial for achieving high energy storage density and efficiency.The Sr_(4.5−x)Ba_(x)Sm_(0.5)Zr_(0.5)Nb_(9.5)O_(30)(x=3.5)dielectric ceramic displayed a ferroelectric/paraelectric transition near room temperature.Subsequent ferroelectric testing revealed large energy storage density(Wrec=4.31 J·cm^(−3))and high efficiency(η=93.8%)at 310 kV·cm−1.Furthermore,Sr_(4.5−x)Ba_(x)Sm_(0.5)Zr_(0.5)Nb_(9.5)O_(30)(x=4.5)exhibited higher breakdown field strength due to its large resistivity and small grain size.This led to energy storage density of approximately 5.3 J·cm^(−3)at 460 kV·cm^(−1).Additionally,Sr_(4.5−x)Ba_(x)Sm_(0.5)Zr_(0.5)Nb_(9.5)O_(30)(x=3.5)demonstrated current density(CD)of approximately 713.38 A·cm^(−2)and power density(PD)of approximately 87.51 MW·cm^(−3),with ultrafast discharge time of 34 ns and excellent discharge energy density(Wdis)of approximately 2.27 J·cm^(−3).Overall,this study presents a promising approach for developing dielectric ceramic materials that hold potential for applications in innovative pulsed power components.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant No.52272119,51872177)the Natural Science Basic Research Plan in the Shaanxi Province of China(Grant No.2021ZDLSF06-03,2021JM-201)+1 种基金the Fundamental Research Funds for the Central Universities(Program No.GK202002014)the Fondamental Innovation Project in School of Materials Science and Engineering(SNNU).
文摘Lead-free relaxor ceramics(1−x)K_(0.5)Na_(0.5)NbO_(3)−xBi(Mn_(0.5)Ni_(0.5))O_(3)((1−x)KNN-xBMN)with considerable charge-discharge characteristics and energy storage properties were prepared by a solid state method.Remarkable,a BMN doping level of 0.04,0.96KNN-0.04BMN ceramic obtained good energy storage performance with acceptable energy storage density Wrec of 1.826 J/cm^(3) and energy storage efficiencyηof 77.4%,as well as good frequency stability(1-500 Hz)and fatigue resistance(1-5000 cycles).Meanwhile,a satisfactory charge-discharge performance with power density PD~98.90 MW/cm^(3),discharge time t0.9<70 ns and temperature stability(30-180°C)was obtained in 0.96KNN-0.04BMN ceramic.The small grain size(~150 nm)and the high polarizability of Bi3+are directly related to its good energy storage capacity.This work proposes a feasible approach for lead-free KNN-based ceramics to achieve high-energy storage and ultra-fast charge-discharge performance as well as candidate materials for the application of advanced high-temperature pulse capacitors.
基金the National Basic Research Program of China (Grant No. 2006CB806000)
文摘Neutral fragments of methane were performed using femetosecond laser at an intensity of 1013-14W/cm2. A new mechanism of neutral dissociation is proposed in this work. The methane molecule is excited to super-excited states,in which it would dissociate into neutral fragments. We made Morse type potential energy surfaces for the super-excited molecules. Furthermore,we investigated the dissociation dy-namics of the super-excited states by using quasi-classical trajectory (QCT) method. The results thus interpret the neutral dissociation of the methane molecule in the ultra-fast laser pulse.
