High-performance metal additive manufacturing （AM） has been extensively investigated in recent years because of its unique advantages over traditional manufacturing processes. AM has been applied to form complex com...High-performance metal additive manufacturing （AM） has been extensively investigated in recent years because of its unique advantages over traditional manufacturing processes. AM has been applied to form complex components of Ti, Fe or Ni alloys. However, for other nonferrous alloys such as AI alloys, Mg alloys and Cu alloys, AM may not be appropriate because of its melting nature during processing by laser, electron beam, and/or arc. Cold spraying （CS） has been widely accepted as a promising solid-state coating technique in last decade for its mass production of high-quality metals and alloys, and/or metal matrix composites coatings. It is now recognized as a useful and powerful tool for AM, but the related research work has just started. This review summarized the literature on the state-of-the-art and problems for CS as an AM and repairing technique.展开更多
As the fifth-generation(5G)mobile communication network may not meet the requirements of emerging technologies and applications,including ubiquitous coverage,industrial internet of things(IIoT),ubiquitous artificial i...As the fifth-generation(5G)mobile communication network may not meet the requirements of emerging technologies and applications,including ubiquitous coverage,industrial internet of things(IIoT),ubiquitous artificial intelligence(AI),digital twins(DT),etc.,this paper aims to explore a novel space-air-ground integrated network(SAGIN)architecture to support these new requirements for the sixth-generation(6G)mobile communication network in a flexible,low-latency and efficient manner.Specifically,we first review the evolution of the mobile communication network,followed by the application and technology requirements of 6G.Then the current 5G non-terrestrial network(NTN)architecture in supporting the new requirements is deeply analyzed.After that,we proposes a new flexible,low-latency and flat SAGIN architecture,and presents corresponding use cases.Finally,the future research directions are discussed.展开更多
Many measurements of B decays involve admixtures of B hadrons. Previously we arbitrarily included such admixtures in the B±section, but because of their importance we have created two new sections：
The 2050 carbon-neutral vision spawns a novel energy structure revolution,and the construction of the future energy structure is based on equipment innovation.Insulating material,as the core of electrical power equipm...The 2050 carbon-neutral vision spawns a novel energy structure revolution,and the construction of the future energy structure is based on equipment innovation.Insulating material,as the core of electrical power equipment and electrified transportation asset,faces unprecedented challenges and opportunities.The goal of carbon neutral and the urgent need for innovation in electric power equipment and electrification assets are first discussed.The engineering challenges constrained by the insulation system in future electric power equipment/devices and electrified transportation assets are investigated.Insulating materials,including intelligent insulating material,high thermal conductivity insulating material,high energy storage density insulating material,extreme environment resistant insulating material,and environmental-friendly insulating material,are cat-egorised with their scientific issues,opportunities and challenges under the goal of carbon neutrality being discussed.In the context of carbon neutrality,not only improves the understanding of the insulation problems from a macro level,that is,electrical power equipment and electrified transportation asset,but also offers opportunities,remaining issues and challenges from the insulating material level.It is hoped that this paper en-visions the challenges regarding design and reliability of insulations in electrical equipment and electric vehicles in the context of policies towards carbon neutrality rules.The authors also hope that this paper can be helpful in future development and research of novel insulating materials,which promote the realisation of the carbon-neutral vision.展开更多
Because the deployable structures are complex multi-loop structures and methods of derivation which lead to simpler kinematic and dynamic equations of motion are the subject of research effort, the kinematics and dyna...Because the deployable structures are complex multi-loop structures and methods of derivation which lead to simpler kinematic and dynamic equations of motion are the subject of research effort, the kinematics and dynamics of deployable structures with scissor-like-elements are presented based on screw theory and the principle of virtual work respectively. According to the geometric characteristic of the deployable structure examined, the basic structural unit is the common scissor-like-element（SLE）. First, a spatial deployable structure, comprised of three SLEs, is defined, and the constraint topology graph is obtained. The equations of motion are then derived based on screw theory and the geometric nature of scissor elements. Second, to develop the dynamics of the whole deployable structure, the local coordinates of the SLEs and the Jacobian matrices of the center of mass of the deployable structure are derived. Then, the equivalent forces are assembled and added in the equations of motion based on the principle of virtual work. Finally, dynamic behavior and unfolded process of the deployable structure are simulated. Its figures of velocity, acceleration and input torque are obtained based on the simulate results. Screw theory not only provides an efficient solution formulation and theory guidance for complex multi-closed loop deployable structures, but also extends the method to solve dynamics of deployable structures. As an efficient mathematical tool, the simper equations of motion are derived based on screw theory.展开更多
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,283 new measurements from 899 papers, we list, evaluate, and average measured properties of gauge bosons and the ...The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,283 new measurements from 899 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as heavy neutrinos, supersymmetric and technicolor particles, axions, dark photons, etc. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as Supersymmetry, Extra Dimensions, Particle Detectors, Probability, and Statistics. Among the 112 reviews are many that are new or heavily revised including those on： Dark Energy, Higgs Boson Physics, Electroweak Model, Neutrino Cross Section Measurements, Monte Carlo Neutrino Generators, Top Quark, Dark Matter, Dynamical Electroweak Symmetry Breaking, Accelerator Physics of Colliders, High-Energy Collider Parameters, Big Bang Nucleosynthesis, Astrophysical Constants and Cosmological Parameters. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews （and errata） are also available on the Particle Data Group website： http ：//pdg. lbl. gov.展开更多
Galloping based piezoelectric energy harvester is a kind of micro-environmental energy harvesting device based on flowinduced vibrations.A novel tristable galloping-based piezoelectric energy harvester is constructed ...Galloping based piezoelectric energy harvester is a kind of micro-environmental energy harvesting device based on flowinduced vibrations.A novel tristable galloping-based piezoelectric energy harvester is constructed by introducing a nonlinear magnetic force on the traditional galloping-based piezoelectric energy harvester.Based on Euler-Bernoulli beam theory and Kirchhoff’s law,the corresponding aero-electromechanical model is proposed and validated by a series of wind tunnel experiments.The parametric study is performed to analyse the response of the tristable galloping-based piezoelectric energy harvester.Numerical results show that comparing with the galloping-based piezoelectric energy harvester,the mechanism of the tristable galloping-based piezoelectric energy harvester is more complex.With the increase of a wind speed,the vibration of the bluff body passes through three branches:intra-well oscillations,chaotic oscillations,and inter-well oscillations.The threshold wind speed of the presented harvester for efficiently harvesting energy is 1.0 m/s,which is decreased by 33% compared with the galloping-based piezoelectric energy harvester.The maximum output power of the presented harvester is 0.73 mW at 7.0 m/s wind speed,which is increased by 35.3%.Compared with the traditional galloping-based piezoelectric energy harvester,the presented tristable galloping-based piezoelectric energy harvester has a better energy harvesting performance from flow-induced vibrations.展开更多
In this paper, a method to design bird-strike-resistant aircraft structures is presented and illustrated through examples. The focus is on bird strike experiments and simulations. The explicit finite element software ...In this paper, a method to design bird-strike-resistant aircraft structures is presented and illustrated through examples. The focus is on bird strike experiments and simulations. The explicit finite element software PAM-CRASH is employed to conduct bird strike simulations, and a coupled Smooth Particles Hydrodynamic（SPH） and Finite Element（FE） method is used to simulate the interaction between a bird and a target structure. The SPH method is explained, and an SPH bird model is established. Constitutive models for various structural materials, such as aluminum alloys, composite materials, honeycomb, and foam materials that are used in aircraft structures,are presented, and model parameters are identified by conducting various material tests. Good agreements between simulation results and experimental data suggest that the numerical model is capable of predicting the dynamic responses of various aircraft structures under a bird strike,and numerical simulation can be used as a tool to design bird-strike-resistant aircraft structures.展开更多
Despite an increase in application spectrum of rare earth elements in agriculture, all studies show that the suitable accumulation of rare earth elements can improve the crop seedling growth, but there is little resea...Despite an increase in application spectrum of rare earth elements in agriculture, all studies show that the suitable accumulation of rare earth elements can improve the crop seedling growth, but there is little research about REEs on physiological mechanisms of crops at reproductive stages. Therefore, this study was conducted to examine the possible potential benefits of lanthanum chloride(LaCl3) on the senescence and grain yield responses of maize. In this study, maize seeds were pre-treated by soaking with LaCl3 at the concentrations of 0(CK), 400(LC1), 800(LC2) and 1200(LC3) μmol/L, to evaluate its effect on the green leaf area, chlorophyll contents, photosynthesis, antioxidants, endogenous hormones in the later crop growth stages. The results show that LC1 and LC2 treatments evidently increase green leaf area, above ground dry biomass, accompanied by a distinct increase in the chlorophyll contents, and photo synthetic capacity, which promote the ear characteristics and grain yield of maize. In addition, LC1 and LC2 treatments simultaneously increase the activities of antioxidants, including superoxide dismutases, catalases, peroxidases, soluble protein, and enhanced levels of auxin, gibberellin and zeatin,following a dose-response tendency. Themalondialdehyde and abscisic acid levels transiently increase with the progression in the growth stage of the crop but are markedly decreased at LC1 and LC2 treatments, while LC3 treatment has no significant effect on malondialdehyde and even accelerates the accumulation of abscisic acid in maize leaves. Our data suggest that seed priming with LaCl3 at a suitable concentration range(400-800 μmol/L) can prolong the functional periods of leaves, increase photosynthetic capacity, enhance antioxidant activity, and alter endogenous hormone levels at reproductive stages, resulting in delaying leaf senescence rate and increasing yield. However, the moderate concentration of LaCl3 for maize is LC2(800 μmol/L), and can be effectively used to improve grain yield of maize.展开更多
The estimation of generalized exponential distribution based on progressive censoring with binomial removals is presented, where the number of units removed at each failure time follows a binomial distribution. Maximu...The estimation of generalized exponential distribution based on progressive censoring with binomial removals is presented, where the number of units removed at each failure time follows a binomial distribution. Maximum likelihood estimators of the parameters and their confidence intervals are derived. The expected time required to complete the life test under this censoring scheme is investigated. Finally, the numerical examples are given to illustrate some theoretical results by means of Monte-Carlo simulation.展开更多
In this paper, a static weapon target assignment（WTA）problem is studied. As a critical problem in cooperative air combat,outcome of WTA directly influences the battle. Along with the cost of weapons rising rapidly, ...In this paper, a static weapon target assignment（WTA）problem is studied. As a critical problem in cooperative air combat,outcome of WTA directly influences the battle. Along with the cost of weapons rising rapidly, it is indispensable to design a target assignment model that can ensure minimizing targets survivability and weapons consumption simultaneously. Afterwards an algorithm named as improved artificial fish swarm algorithm-improved harmony search algorithm（IAFSA-IHS） is proposed to solve the problem. The effect of the proposed algorithm is demonstrated in numerical simulations, and results show that it performs positively in searching the optimal solution and solving the WTA problem.展开更多
Zanthoxylum bungeanum is an important spice and medicinal plant that is unique for its accumulation of abundant secondary metabolites,which create a characteristic aroma and tingling sensation in the mouth.Owing to th...Zanthoxylum bungeanum is an important spice and medicinal plant that is unique for its accumulation of abundant secondary metabolites,which create a characteristic aroma and tingling sensation in the mouth.Owing to the high proportion of repetitive sequences,high heterozygosity,and increased chromosome number of Z.bungeanum,the assembly of its chromosomal pseudomolecules is extremely challenging.Here,we present a genome sequence for Z.bungeanum,with a dramatically expanded size of 4.23 Gb,assembled into 68 chromosomes.This genome is approximately tenfold larger than that of its close relative Citrus sinensis.After the divergence of Zanthoxylum and Citrus,the lineage-specific whole-genome duplication event q-WGD approximately 26.8 million years ago(MYA)and the recent transposable element(TE)burst~6.41 MYA account for the substantial genome expansion in Z.bungeanum.The independent Zanthoxylum-specific WGD event was followed by numerous fusion/fission events that shaped the genomic architecture.Integrative genomic and transcriptomic analyses suggested that prominent speciesspecific gene family expansions and changes in gene expression have shaped the biosynthesis of sanshools,terpenoids,and anthocyanins,which contribute to the special flavor and appearance of Z.bungeanum.In summary,the reference genome provides a valuable model for studying the impact of WGDs with recent TE activity on gene gain and loss and genome reconstruction and provides resources to accelerate Zanthoxylum improvement.展开更多
Phase engineering is an important strategy to modulate the electronic structure of molybdenum disulfide(MoS_(2)).MoS_(2)-based composites are usually used for the electromagnetic wave(EMW)absorber,but the effect of di...Phase engineering is an important strategy to modulate the electronic structure of molybdenum disulfide(MoS_(2)).MoS_(2)-based composites are usually used for the electromagnetic wave(EMW)absorber,but the effect of different phases on the EMW absorbing performance,such as 1T and 2H phase,is still not studied.In this work,micro-1T/2H MoS_(2) is achieved via a facile one-step hydrother-mal route,in which the 1T phase is induced by the intercalation of guest molecules and ions.The EMW absorption mechanism of single MoS_(2) is revealed by presenting a comparative study between 1T/2H MoS_(2) and 2H MoS_(2).As a result,1T/2H MoS_(2) with the matrix loading of 15%exhibits excellent microwave absorption property than 2H MoS_(2).Furthermore,taking the advantage of 1T/2H MoS_(2),a flexible EMW absorbers that ultrathin 1T/2H MoS_(2)grown on the carbon fiber also performs outstanding performance only with the matrix loading of 5%.This work offers necessary reference to improve microwave absorption performance by phase engineering and design a new type of flexible electromagnetic wave absorption material to apply for the portable microwave absorption electronic devices.展开更多
A bounded,mono-peak,and symmetrically distributed probability density function, called λ-PDF,together with the Gegenbauer polynomial approximation,is used in dynamic response problems of random structures.The λ-PDF ...A bounded,mono-peak,and symmetrically distributed probability density function, called λ-PDF,together with the Gegenbauer polynomial approximation,is used in dynamic response problems of random structures.The λ-PDF can reasonably model a variety of random parameters in engineering random structures.The Gegenbauer polynomial approximation can be viewed as a new extension of the weighted residual method into the random space.Both of them can be easily used by scientists and engineers,and applied to a variety of response problems of random structures.The numerical example shows the effectiveness of the proposed method to study dynamic phenomena in random structures.展开更多
Based on Kohler’s ternary solution model and Miedema’s model for calculating the formation heat of binary solution, the integral equation was established for calculating the activity coefficients in ternary alloys a...Based on Kohler’s ternary solution model and Miedema’s model for calculating the formation heat of binary solution, the integral equation was established for calculating the activity coefficients in ternary alloys and intermetallics. The activity coefficients for components in alloy Ti-5Al-2.5Sn, Ti-6Al-4V and intermetallics TiAl, Ti3Al and Ti2AlNb were calculated with the equations. The calculated data coincide well with the experimental ones found in literatures. According to the calculated activity coefficients and activities, it can be predicted that the interfacial reaction in SiC/Ti3Al composite is more severe than that in composites SiC/Ti2AlNb and SiC/TiAl.展开更多
Direct generation of chirp-free solitons without external compression in normal-dispersion fiber lasers is a long-term challenge in ultrafast optics.We demonstrate near-chirp-free solitons with distinct spectral sideb...Direct generation of chirp-free solitons without external compression in normal-dispersion fiber lasers is a long-term challenge in ultrafast optics.We demonstrate near-chirp-free solitons with distinct spectral sidebands in normaldispersion hybrid-structure fiber lasers containing a few meters of polarization-maintaining fiber.The bandwidth and duration of the typical mode-locked pulse are 0.74 nm and 1.95 ps,respectively,giving the time-bandwidth product of 0.41 and confirming the near-chirp-free property.Numerical results and theoretical analyses fully reproduce and interpret the experimental observations,and show that the fiber birefringence,normal-dispersion,and nonlinear effect follow a phase-matching principle,enabling the formation of the near-chirp-free soliton.Specifically,the phasematching effect confines the spectrum broadened by self-phase modulation and the saturable absorption effect slims the pulse stretched by normal dispersion.Such pulse is termed as birefringence-managed soliton because its two orthogonal-polarized components propagate in an unsymmetrical“X”manner inside the polarization-maintaining fiber,partially compensating the group delay difference induced by the chromatic dispersion and resulting in the selfconsistent evolution.The property and formation mechanism of birefringence-managed soliton fundamentally differ from other types of pulses in mode-locked fiber lasers,which will open new research branches in laser physics,soliton mathematics,and their related applications.展开更多
“A Craftsman Must Sharpen His Tools to Do His Job,”said Confucius.Nuclear detection and readout techniques are the foundation of particle physics,nuclear physics,and particle astrophysics to reveal the nature of the...“A Craftsman Must Sharpen His Tools to Do His Job,”said Confucius.Nuclear detection and readout techniques are the foundation of particle physics,nuclear physics,and particle astrophysics to reveal the nature of the universe.Also,they are being increasingly used in other disciplines like nuclear power generation,life sciences,environmental sciences,medical sciences,etc.The article reviews the short history,recent development,and trend of nuclear detection and readout techniques,covering Semiconductor Detector,Gaseous Detector,Scintillation Detector,Cherenkov Detector,Transition Radiation Detector,and Readout Techniques.By explaining the principle and using examples,we hope to help the interested reader underst and this research field and bring exciting information to the community.展开更多
The components of the rock, the pigments, the gold foils and the adhesive of One Thousand Hand Buddha in Dazu stone sculptures, Chongqing, China, have been analyzed by X-ray diffraction (XRD), X-ray fluorescence (XRF)...The components of the rock, the pigments, the gold foils and the adhesive of One Thousand Hand Buddha in Dazu stone sculptures, Chongqing, China, have been analyzed by X-ray diffraction (XRD), X-ray fluorescence (XRF), infrared spectroscopy (IR), energy dispersive X-ray analysis (EDX) and fiber optics reflectance spectros-copy (FORS). Furthermore, the weathering and degeneration of One Thousand Hand Buddha have been discussed and the protective methods have been provided. In this work some useful information to study on conservation of stone relics is given.展开更多
基金the financial support from the National Key Research and Development Program of China (2016YFB0701203)the National Natural Science Foundation of China (51574196)+1 种基金the fund of SAST (SAST2016043)the 111 Project (B08040)
文摘High-performance metal additive manufacturing （AM） has been extensively investigated in recent years because of its unique advantages over traditional manufacturing processes. AM has been applied to form complex components of Ti, Fe or Ni alloys. However, for other nonferrous alloys such as AI alloys, Mg alloys and Cu alloys, AM may not be appropriate because of its melting nature during processing by laser, electron beam, and/or arc. Cold spraying （CS） has been widely accepted as a promising solid-state coating technique in last decade for its mass production of high-quality metals and alloys, and/or metal matrix composites coatings. It is now recognized as a useful and powerful tool for AM, but the related research work has just started. This review summarized the literature on the state-of-the-art and problems for CS as an AM and repairing technique.
基金supported in part by the National Key Research and Development Program under grant number 2020YFB1806800the Beijing Natural Science Foundation under grant number L212003the National Natural Science Foundation of China(NSFC)under grant numbers 62171010 and 61827901.
文摘As the fifth-generation(5G)mobile communication network may not meet the requirements of emerging technologies and applications,including ubiquitous coverage,industrial internet of things(IIoT),ubiquitous artificial intelligence(AI),digital twins(DT),etc.,this paper aims to explore a novel space-air-ground integrated network(SAGIN)architecture to support these new requirements for the sixth-generation(6G)mobile communication network in a flexible,low-latency and efficient manner.Specifically,we first review the evolution of the mobile communication network,followed by the application and technology requirements of 6G.Then the current 5G non-terrestrial network(NTN)architecture in supporting the new requirements is deeply analyzed.After that,we proposes a new flexible,low-latency and flat SAGIN architecture,and presents corresponding use cases.Finally,the future research directions are discussed.
文摘Many measurements of B decays involve admixtures of B hadrons. Previously we arbitrarily included such admixtures in the B±section, but because of their importance we have created two new sections：
文摘The 2050 carbon-neutral vision spawns a novel energy structure revolution,and the construction of the future energy structure is based on equipment innovation.Insulating material,as the core of electrical power equipment and electrified transportation asset,faces unprecedented challenges and opportunities.The goal of carbon neutral and the urgent need for innovation in electric power equipment and electrification assets are first discussed.The engineering challenges constrained by the insulation system in future electric power equipment/devices and electrified transportation assets are investigated.Insulating materials,including intelligent insulating material,high thermal conductivity insulating material,high energy storage density insulating material,extreme environment resistant insulating material,and environmental-friendly insulating material,are cat-egorised with their scientific issues,opportunities and challenges under the goal of carbon neutrality being discussed.In the context of carbon neutrality,not only improves the understanding of the insulation problems from a macro level,that is,electrical power equipment and electrified transportation asset,but also offers opportunities,remaining issues and challenges from the insulating material level.It is hoped that this paper en-visions the challenges regarding design and reliability of insulations in electrical equipment and electric vehicles in the context of policies towards carbon neutrality rules.The authors also hope that this paper can be helpful in future development and research of novel insulating materials,which promote the realisation of the carbon-neutral vision.
基金Supported by National Natural Science Foundation of China(Grant No.51175422)
文摘Because the deployable structures are complex multi-loop structures and methods of derivation which lead to simpler kinematic and dynamic equations of motion are the subject of research effort, the kinematics and dynamics of deployable structures with scissor-like-elements are presented based on screw theory and the principle of virtual work respectively. According to the geometric characteristic of the deployable structure examined, the basic structural unit is the common scissor-like-element（SLE）. First, a spatial deployable structure, comprised of three SLEs, is defined, and the constraint topology graph is obtained. The equations of motion are then derived based on screw theory and the geometric nature of scissor elements. Second, to develop the dynamics of the whole deployable structure, the local coordinates of the SLEs and the Jacobian matrices of the center of mass of the deployable structure are derived. Then, the equivalent forces are assembled and added in the equations of motion based on the principle of virtual work. Finally, dynamic behavior and unfolded process of the deployable structure are simulated. Its figures of velocity, acceleration and input torque are obtained based on the simulate results. Screw theory not only provides an efficient solution formulation and theory guidance for complex multi-closed loop deployable structures, but also extends the method to solve dynamics of deployable structures. As an efficient mathematical tool, the simper equations of motion are derived based on screw theory.
基金supported by the Director,Office of Science,Office of High Energy Physics of the U.S.Department of Energy under Contract No.DE-AC02-05CH11231the U.S.National Science Foundation under Agreement No.PHY-0652989+3 种基金the European Laboratory for Particle Physics(CERN)an implementing arrangement between the governments of Japan(MEXT:Ministry of Education,Culture,Sports,Science and Technology)and the United States(DOE)on cooperative research and developmentthe Italian National Institute of Nuclear Physics(INFN)B.C.F.was supported by the U.S.National Science Foundation Grant PHY-1214082
文摘The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,283 new measurements from 899 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as heavy neutrinos, supersymmetric and technicolor particles, axions, dark photons, etc. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as Supersymmetry, Extra Dimensions, Particle Detectors, Probability, and Statistics. Among the 112 reviews are many that are new or heavily revised including those on： Dark Energy, Higgs Boson Physics, Electroweak Model, Neutrino Cross Section Measurements, Monte Carlo Neutrino Generators, Top Quark, Dark Matter, Dynamical Electroweak Symmetry Breaking, Accelerator Physics of Colliders, High-Energy Collider Parameters, Big Bang Nucleosynthesis, Astrophysical Constants and Cosmological Parameters. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews （and errata） are also available on the Particle Data Group website： http ：//pdg. lbl. gov.
基金supported by the National Natural Science Foundation of China(Grants 51606171,51977196,and 11802237)China Postdoctoral Science Foundation(Grant 2019M652565).
文摘Galloping based piezoelectric energy harvester is a kind of micro-environmental energy harvesting device based on flowinduced vibrations.A novel tristable galloping-based piezoelectric energy harvester is constructed by introducing a nonlinear magnetic force on the traditional galloping-based piezoelectric energy harvester.Based on Euler-Bernoulli beam theory and Kirchhoff’s law,the corresponding aero-electromechanical model is proposed and validated by a series of wind tunnel experiments.The parametric study is performed to analyse the response of the tristable galloping-based piezoelectric energy harvester.Numerical results show that comparing with the galloping-based piezoelectric energy harvester,the mechanism of the tristable galloping-based piezoelectric energy harvester is more complex.With the increase of a wind speed,the vibration of the bluff body passes through three branches:intra-well oscillations,chaotic oscillations,and inter-well oscillations.The threshold wind speed of the presented harvester for efficiently harvesting energy is 1.0 m/s,which is decreased by 33% compared with the galloping-based piezoelectric energy harvester.The maximum output power of the presented harvester is 0.73 mW at 7.0 m/s wind speed,which is increased by 35.3%.Compared with the traditional galloping-based piezoelectric energy harvester,the presented tristable galloping-based piezoelectric energy harvester has a better energy harvesting performance from flow-induced vibrations.
基金supported by Natural Science Foundation of China (No.11472225)
文摘In this paper, a method to design bird-strike-resistant aircraft structures is presented and illustrated through examples. The focus is on bird strike experiments and simulations. The explicit finite element software PAM-CRASH is employed to conduct bird strike simulations, and a coupled Smooth Particles Hydrodynamic（SPH） and Finite Element（FE） method is used to simulate the interaction between a bird and a target structure. The SPH method is explained, and an SPH bird model is established. Constitutive models for various structural materials, such as aluminum alloys, composite materials, honeycomb, and foam materials that are used in aircraft structures,are presented, and model parameters are identified by conducting various material tests. Good agreements between simulation results and experimental data suggest that the numerical model is capable of predicting the dynamic responses of various aircraft structures under a bird strike,and numerical simulation can be used as a tool to design bird-strike-resistant aircraft structures.
基金Project supported by the High Technology Research and Development Program of China(2013AA102902)the National Key Technology Support Program of China(2012BAD09B03)
文摘Despite an increase in application spectrum of rare earth elements in agriculture, all studies show that the suitable accumulation of rare earth elements can improve the crop seedling growth, but there is little research about REEs on physiological mechanisms of crops at reproductive stages. Therefore, this study was conducted to examine the possible potential benefits of lanthanum chloride(LaCl3) on the senescence and grain yield responses of maize. In this study, maize seeds were pre-treated by soaking with LaCl3 at the concentrations of 0(CK), 400(LC1), 800(LC2) and 1200(LC3) μmol/L, to evaluate its effect on the green leaf area, chlorophyll contents, photosynthesis, antioxidants, endogenous hormones in the later crop growth stages. The results show that LC1 and LC2 treatments evidently increase green leaf area, above ground dry biomass, accompanied by a distinct increase in the chlorophyll contents, and photo synthetic capacity, which promote the ear characteristics and grain yield of maize. In addition, LC1 and LC2 treatments simultaneously increase the activities of antioxidants, including superoxide dismutases, catalases, peroxidases, soluble protein, and enhanced levels of auxin, gibberellin and zeatin,following a dose-response tendency. Themalondialdehyde and abscisic acid levels transiently increase with the progression in the growth stage of the crop but are markedly decreased at LC1 and LC2 treatments, while LC3 treatment has no significant effect on malondialdehyde and even accelerates the accumulation of abscisic acid in maize leaves. Our data suggest that seed priming with LaCl3 at a suitable concentration range(400-800 μmol/L) can prolong the functional periods of leaves, increase photosynthetic capacity, enhance antioxidant activity, and alter endogenous hormone levels at reproductive stages, resulting in delaying leaf senescence rate and increasing yield. However, the moderate concentration of LaCl3 for maize is LC2(800 μmol/L), and can be effectively used to improve grain yield of maize.
基金supported by the National Natural Science Foundation of China(70471057)
文摘The estimation of generalized exponential distribution based on progressive censoring with binomial removals is presented, where the number of units removed at each failure time follows a binomial distribution. Maximum likelihood estimators of the parameters and their confidence intervals are derived. The expected time required to complete the life test under this censoring scheme is investigated. Finally, the numerical examples are given to illustrate some theoretical results by means of Monte-Carlo simulation.
基金supported by the National Natural Science Foundation of China(61472441)
文摘In this paper, a static weapon target assignment（WTA）problem is studied. As a critical problem in cooperative air combat,outcome of WTA directly influences the battle. Along with the cost of weapons rising rapidly, it is indispensable to design a target assignment model that can ensure minimizing targets survivability and weapons consumption simultaneously. Afterwards an algorithm named as improved artificial fish swarm algorithm-improved harmony search algorithm（IAFSA-IHS） is proposed to solve the problem. The effect of the proposed algorithm is demonstrated in numerical simulations, and results show that it performs positively in searching the optimal solution and solving the WTA problem.
基金This research was financially supported by the National Key R&D Program of China(2018YFD1000605)the Tianjin Science Fund for Distinguished Young Scholars(18JCJQJC48300).
文摘Zanthoxylum bungeanum is an important spice and medicinal plant that is unique for its accumulation of abundant secondary metabolites,which create a characteristic aroma and tingling sensation in the mouth.Owing to the high proportion of repetitive sequences,high heterozygosity,and increased chromosome number of Z.bungeanum,the assembly of its chromosomal pseudomolecules is extremely challenging.Here,we present a genome sequence for Z.bungeanum,with a dramatically expanded size of 4.23 Gb,assembled into 68 chromosomes.This genome is approximately tenfold larger than that of its close relative Citrus sinensis.After the divergence of Zanthoxylum and Citrus,the lineage-specific whole-genome duplication event q-WGD approximately 26.8 million years ago(MYA)and the recent transposable element(TE)burst~6.41 MYA account for the substantial genome expansion in Z.bungeanum.The independent Zanthoxylum-specific WGD event was followed by numerous fusion/fission events that shaped the genomic architecture.Integrative genomic and transcriptomic analyses suggested that prominent speciesspecific gene family expansions and changes in gene expression have shaped the biosynthesis of sanshools,terpenoids,and anthocyanins,which contribute to the special flavor and appearance of Z.bungeanum.In summary,the reference genome provides a valuable model for studying the impact of WGDs with recent TE activity on gene gain and loss and genome reconstruction and provides resources to accelerate Zanthoxylum improvement.
基金the National Natural Science Foundation of China(No.51672222)Joint Fund Project-Enterprise-Shaanxi Coal Joint Fund Project(2019JLM-32)+2 种基金Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(CX202054)the Graduate innovation team of Northwestern Polytechnical Universitythe Analysis and Testing Center of Northwestern Polytechnical University for their technical assistance in SEM(Verios G4).
文摘Phase engineering is an important strategy to modulate the electronic structure of molybdenum disulfide(MoS_(2)).MoS_(2)-based composites are usually used for the electromagnetic wave(EMW)absorber,but the effect of different phases on the EMW absorbing performance,such as 1T and 2H phase,is still not studied.In this work,micro-1T/2H MoS_(2) is achieved via a facile one-step hydrother-mal route,in which the 1T phase is induced by the intercalation of guest molecules and ions.The EMW absorption mechanism of single MoS_(2) is revealed by presenting a comparative study between 1T/2H MoS_(2) and 2H MoS_(2).As a result,1T/2H MoS_(2) with the matrix loading of 15%exhibits excellent microwave absorption property than 2H MoS_(2).Furthermore,taking the advantage of 1T/2H MoS_(2),a flexible EMW absorbers that ultrathin 1T/2H MoS_(2)grown on the carbon fiber also performs outstanding performance only with the matrix loading of 5%.This work offers necessary reference to improve microwave absorption performance by phase engineering and design a new type of flexible electromagnetic wave absorption material to apply for the portable microwave absorption electronic devices.
基金The project supported by the National Natural Science Foundation of China (10332030)
文摘A bounded,mono-peak,and symmetrically distributed probability density function, called λ-PDF,together with the Gegenbauer polynomial approximation,is used in dynamic response problems of random structures.The λ-PDF can reasonably model a variety of random parameters in engineering random structures.The Gegenbauer polynomial approximation can be viewed as a new extension of the weighted residual method into the random space.Both of them can be easily used by scientists and engineers,and applied to a variety of response problems of random structures.The numerical example shows the effectiveness of the proposed method to study dynamic phenomena in random structures.
文摘Based on Kohler’s ternary solution model and Miedema’s model for calculating the formation heat of binary solution, the integral equation was established for calculating the activity coefficients in ternary alloys and intermetallics. The activity coefficients for components in alloy Ti-5Al-2.5Sn, Ti-6Al-4V and intermetallics TiAl, Ti3Al and Ti2AlNb were calculated with the equations. The calculated data coincide well with the experimental ones found in literatures. According to the calculated activity coefficients and activities, it can be predicted that the interfacial reaction in SiC/Ti3Al composite is more severe than that in composites SiC/Ti2AlNb and SiC/TiAl.
基金This work was funded by the National Key R&D Program of China under Grant No.2017YFA0303800the National Natural Science Foundation of China under Grant No.11874300+2 种基金11634010the Fundamental Research Funds for the Central Universities under Grant No.3102019JC008,3102019PY002the Natural Science Foundation of Shaanxi Province under Grant No.2019JQ-447.
文摘Direct generation of chirp-free solitons without external compression in normal-dispersion fiber lasers is a long-term challenge in ultrafast optics.We demonstrate near-chirp-free solitons with distinct spectral sidebands in normaldispersion hybrid-structure fiber lasers containing a few meters of polarization-maintaining fiber.The bandwidth and duration of the typical mode-locked pulse are 0.74 nm and 1.95 ps,respectively,giving the time-bandwidth product of 0.41 and confirming the near-chirp-free property.Numerical results and theoretical analyses fully reproduce and interpret the experimental observations,and show that the fiber birefringence,normal-dispersion,and nonlinear effect follow a phase-matching principle,enabling the formation of the near-chirp-free soliton.Specifically,the phasematching effect confines the spectrum broadened by self-phase modulation and the saturable absorption effect slims the pulse stretched by normal dispersion.Such pulse is termed as birefringence-managed soliton because its two orthogonal-polarized components propagate in an unsymmetrical“X”manner inside the polarization-maintaining fiber,partially compensating the group delay difference induced by the chromatic dispersion and resulting in the selfconsistent evolution.The property and formation mechanism of birefringence-managed soliton fundamentally differ from other types of pulses in mode-locked fiber lasers,which will open new research branches in laser physics,soliton mathematics,and their related applications.
基金supported by the National Natural Science Foundation of China(No.12222512,U2032209,12075045,12335011,1875097,11975257,62074146,11975115,12205374,12305210,11975292,12005276,12005278,12375193,12227805,12235012,12375191,12005279)the National Key Research and Development Program of China(2021YFA1601300)+13 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(XDB34000000)the CAS Pioneer Hundred Talent Programthe CAS“Light of West China”Programthe Natural Science Foundation of Liaoning Province(No.101300261)the Dalian Science and Technology Innovation Fund(2023JJ12GX013)the Special Projects of the Central Government in Guidance of Local Science and Technology Development(Research and development of three-dimensional prospecting technology based on Cosmic-ray muons)(YDZX20216200001297)the Science and Technology Planning Project of Gansu(20JR10RA645)the Lanzhou University Talent Cooperation Research Funds sponsored by both Lanzhou City(561121203)the Gansu provincial science and technology plan projects for talents(054000029)the Beijing Natural Science Foundation(No.1232033)the Beijing Hope Run Special Fund of Cancer Foundation of China(No.LC2021B23)the Guangdong Major Project of Basic and Applied Basic Research(No.2020B0301030008)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(No.GJJSTD20210009)the Youth Innovation Promotion Association CAS(2021450)。
文摘“A Craftsman Must Sharpen His Tools to Do His Job,”said Confucius.Nuclear detection and readout techniques are the foundation of particle physics,nuclear physics,and particle astrophysics to reveal the nature of the universe.Also,they are being increasingly used in other disciplines like nuclear power generation,life sciences,environmental sciences,medical sciences,etc.The article reviews the short history,recent development,and trend of nuclear detection and readout techniques,covering Semiconductor Detector,Gaseous Detector,Scintillation Detector,Cherenkov Detector,Transition Radiation Detector,and Readout Techniques.By explaining the principle and using examples,we hope to help the interested reader underst and this research field and bring exciting information to the community.
基金Project supported by the Natural Science Foundation of Shaanxi Province (No. 2001H12).
文摘The components of the rock, the pigments, the gold foils and the adhesive of One Thousand Hand Buddha in Dazu stone sculptures, Chongqing, China, have been analyzed by X-ray diffraction (XRD), X-ray fluorescence (XRF), infrared spectroscopy (IR), energy dispersive X-ray analysis (EDX) and fiber optics reflectance spectros-copy (FORS). Furthermore, the weathering and degeneration of One Thousand Hand Buddha have been discussed and the protective methods have been provided. In this work some useful information to study on conservation of stone relics is given.
