In the field of civil engineering, magnetorheological fluid （MRF） damper-based semi-active control systems have received considerable attention for use in protecting structures from natural hazards such as strong ea...In the field of civil engineering, magnetorheological fluid （MRF） damper-based semi-active control systems have received considerable attention for use in protecting structures from natural hazards such as strong earthquakes and high winds. In this paper, the MRF damper-based semi-active control system is applied to a long-span spatially extended structure and its feasibility is discussed. Meanwhile, a _trust-region method based instantaneous optimal semi-active control algorithm （TIOC） is proposed to improve the performance of the semi-active control system in a multiple damper situation. The proposed TIOC describes the control process as a bounded constraint optimization problem, in which an optimal semi- active control force vector is solved by the trust-region method in every control step to minimize the structural responses. A numerical example of a railway station roof structure installed with MRF-04K dampers is presented. First, a modified Bouc- Wen model is utilized to describe the behavior of the selected MRF-04K damper. Then, two semi-active control systems, including the well-known clipped-optimal controller and the proposed TIOC controller, are considered. Based on the characteristics of the long-span spatially extended structure, the performance of the control system is evaluated under uniform earthquake excitation and travelling-wave excitation with different apparent velocities. The simulation results indicate that the MR fluid damper-based semi-active control systems have the potential to mitigate the responses of full-scale long-span spatially extended structures under earthquake hazards. The superiority of the proposed TIOC controller is demonstrated by comparing its control effectiveness with the clipped-optimal controller for several different cases.展开更多
Accurate identification of influential nodes facilitates the control of rumor propagation and interrupts the spread of computer viruses.Many classical approaches have been proposed by researchers regarding different a...Accurate identification of influential nodes facilitates the control of rumor propagation and interrupts the spread of computer viruses.Many classical approaches have been proposed by researchers regarding different aspects.To explore the impact of location information in depth,this paper proposes an improved global structure model to characterize the influence of nodes.The method considers both the node’s self-information and the role of the location information of neighboring nodes.First,degree centrality of each node is calculated,and then degree value of each node is used to represent self-influence,and degree values of the neighbor layer nodes are divided by the power of the path length,which is path attenuation used to represent global influence.Finally,an extended improved global structure model that considers the nearest neighbor information after combining self-influence and global influence is proposed to identify influential nodes.In this paper,the propagation process of a real network is obtained by simulation with the SIR model,and the effectiveness of the proposed method is verified from two aspects of discrimination and accuracy.The experimental results show that the proposed method is more accurate in identifying influential nodes than other comparative methods with multiple networks.展开更多
Perovskite solar cells (PSCs) employing formamidinium lead iodide (FAPbI_(3)) have shown high efficiency.However,operational stability has been issued due to phase instability of α phase FAPbI_(3) at ambient temperat...Perovskite solar cells (PSCs) employing formamidinium lead iodide (FAPbI_(3)) have shown high efficiency.However,operational stability has been issued due to phase instability of α phase FAPbI_(3) at ambient temperature.Excess precursors in the perovskite precursor solution has been proposed to improve not only power conversion efficiency (PCE) but also device stability.Nevertheless,there is a controversial issue on the beneficial effect on PCE and/or stability between excess FAI and excess PbI_(2).We report here extended X-ray absorption fine structure (EXAFS) of FAPbI_(3) to study local structural change and explain the effect of excess precursors on photovoltaic performance and stability.Perovskite films prepared from the precursor solution with excess PbI_(2)shows better stability than those from the one with excess FAI,despite similar PCE.A rapid phase transition from α phase to non-perovskite δ phase is observed from the perovskite film formed by excess FAI.Furthermore,the (Pb-I) bond distance evaluated by the Pb L_(III)-edge EXAFS study is increased by excess FAI,which is responsible for the phase transition and poor device stability.This work can provide important insight into local structure-stability relation in the FAPbI_(3)-based PSCs.展开更多
A new 3D extended structural compound, （dpdo）2H2{[Cu（2,2＇-bipy）212（P2W18O62）}.SH2O 1 （dpdo = 4,4＇-bipyridine-N,N＇- dioxide; 2,2＇-bipy = 2,2＇-bipyridine）, has been hydrothermally synthesized and characteri...A new 3D extended structural compound, （dpdo）2H2{[Cu（2,2＇-bipy）212（P2W18O62）}.SH2O 1 （dpdo = 4,4＇-bipyridine-N,N＇- dioxide; 2,2＇-bipy = 2,2＇-bipyridine）, has been hydrothermally synthesized and characterized by elemental analyses, IR, TG analyses, cyclic voltammetry, and single-crystal X-my diffraction. Compound 1 is built up of [P2WlsO62]6- cluster as the structural motif covalently linked by [Cu（2,2＇-bipy）2]^2＋ coordination complexes to yield the 1D chains, which axe further in close contact forming a 3D supramolecular framework via aromatic π-π stacking interactions and extensive hydrogen-bonding interactions among polyoxoanions, coordinated 2,2＇-bipy organic ligands, free dpdo organic molecules and lattice water molecules.展开更多
Thin wall samples of high density polyethylene （HDPE） were prepared via injection molding with different injection speeds ranging from 100 mm/s to 1200 mm/s. A significant decrease in the tensile strength and Young...Thin wall samples of high density polyethylene （HDPE） were prepared via injection molding with different injection speeds ranging from 100 mm/s to 1200 mm/s. A significant decrease in the tensile strength and Young＇s modulus was observed with increasing injection speed. In order to investigate the mechanism behind this decrease, the orientation, molecular weight, molecular weight distribution, melt flow rate, crystallinity and crystal morphology of HDPE were characterized using two-dimensional wide-angle X-ray diffraction （2D-WAXD）, gel permeation chromatography （GPC）, capillary rheometry and differential scanning calorimetry （DSC）, respectively. It is demonstrated that the orientation, molecular weight, molecular weight distribution, melt flow rate and crystallinity have no obvious change with increasing injection speed. Nevertheless, the content of extended chain crystals or large folded chain crystals was found to decrease with increasing injection speed. Therefore, it is concluded that the decrease in tensile properties is mainly contributed by the reduced content of extended chain crystals or large folded chain crystals. This study provides industry with valuable information for the application of high speed injection molding.展开更多
Effect of structure parameter n and its coupling with the connection mode among RuO6 octahedra of Srn＋1RUnO3n＋1 （n = 1, 2, ∞） are investigated. The gradually enhanced rotation and tilting effect with increasing n...Effect of structure parameter n and its coupling with the connection mode among RuO6 octahedra of Srn＋1RUnO3n＋1 （n = 1, 2, ∞） are investigated. The gradually enhanced rotation and tilting effect with increasing n are observed in Srn＋1RUnO3n＋1. Besides, the chemical valence of Ru is not changed, while the one of Sr gradually varies with increasing n, which highlights the great contribution of connection mode to the chemical environment. Our results show a strong n dependence on the connection mode between octahedra in Srn＋1RUnO3n＋1 （n = 1, 2, ∞）.展开更多
Lithium-sulfur(Li-S)batteries hold great promise for the next generation of high energy density systems.However,sluggish sulfur conversion and the shuttle effect of polysulfides severely limit their commercial applica...Lithium-sulfur(Li-S)batteries hold great promise for the next generation of high energy density systems.However,sluggish sulfur conversion and the shuttle effect of polysulfides severely limit their commercial applications.Herein,a multifunctional covalent organic framework(Ni-COF)with extendedπ-d conjugated structure was synthesized and used for separator modification to overcome the obstacles in Li-S batteries.Ni-COF inherits the advantages of both COFs and conductive metal-organic frameworks,while compensating for their respective disadvantages.The abundant oxygen-containing groups in Ni-COF act as chemical adsorption sites to inhibit the shuttle effect of polysulfides.The designedπ-d conjugated structure enhances electrical conductivity and provides high-density metal catalytic sites,thereby facilitating the conversion of polysulfides and enhancing the reaction kinetics of Li-S batteries.Consequently,the Li-S batteries with Ni-COF@PP separator exhibit remarkable rate performance of 719 mA h g^(-1)at 4 C,along with a low attenuation rate of 0.087%per cycle over 300 cycles at 1 C.This study proposes a novel strategy for the rational design of COFs in Li-S batteries.展开更多
Synchrotron radiation extended X-ray absorption fine structure(SR EXAFS)was used to study the transformation of coordination and redox state of arsenic(As)in a newly discovered As hyperaccumulator,Pteris vittata L.,wh...Synchrotron radiation extended X-ray absorption fine structure(SR EXAFS)was used to study the transformation of coordination and redox state of arsenic(As)in a newly discovered As hyperaccumulator,Pteris vittata L.,which is considered to have great potential for phytoremediating the As contaminated soil.It is shown that the As in this plant was mainly coordinated with oxygen in thereduced state,As(IIl),and the reduction of As(V)occurred in the root after it was taken up.No oxidationof As(II)was found during the translocation of As,from root to shoot.Only a small amount of As was coordinated with sulfur in root and petiole,but not distinct in pinna.展开更多
Airframe maintenance is traditionally performed at scheduled maintenance stops.The decision to repair a fuselage panel is based on a fixed crack size threshold,which allows to ensure the aircraft safety until the next...Airframe maintenance is traditionally performed at scheduled maintenance stops.The decision to repair a fuselage panel is based on a fixed crack size threshold,which allows to ensure the aircraft safety until the next scheduled maintenance stop.With progress in sensor technology and data processing techniques,structural health monitoring（SHM） systems are increasingly being considered in the aviation industry.SHM systems track the aircraft health state continuously,leading to the possibility of planning maintenance based on an actual state of aircraft rather than on a fixed schedule.This paper builds upon a model-based prognostics framework that the authors developed in their previous work,which couples the Extended Kalman filter（EKF） with a firstorder perturbation（FOP） method.By using the information given by this prognostics method,a novel cost driven predictive maintenance（CDPM） policy is proposed,which ensures the aircraft safety while minimizing the maintenance cost.The proposed policy is formally derived based on the trade-off between probabilities of occurrence of scheduled and unscheduled maintenance.A numerical case study simulating the maintenance process of an entire fleet of aircrafts is implemented.Under the condition of assuring the same safety level,the CDPM is compared in terms of cost with two other maintenance policies：scheduled maintenance and threshold based SHM maintenance.The comparison results show CDPM could lead to significant cost savings.展开更多
The distributed optical fiber sensing technology was used to investigate the fracture behavior of the Epoxy Asphalt Mixture. The spatial distribution and variation of the strain development with crack propagation were...The distributed optical fiber sensing technology was used to investigate the fracture behavior of the Epoxy Asphalt Mixture. The spatial distribution and variation of the strain development with crack propagation were acquired using the brillouin optical time-domain reflectometer through the loading experiments of the composite beam structure. In addition, a finite element model of the composite beam structure was developed to analyze the mechanical responses of the epoxy asphalt mixture using the extended finite element method. The experimental results show that the development of crack propagation becomes instable with the increase of the load, and larger loads will generate deeper cracks. Moreover, the numerical results show that the mechanical response of the crack tip changes with the crack propagation, and the worst areas that subjected to crack damage are located on both sides of the composite beam structure.展开更多
In the seismic analysis of extended structures subject to spatially varying motions,the displacement input model instead of acceleration model is usually adopted for accurate results.In this paper,a more detailed and ...In the seismic analysis of extended structures subject to spatially varying motions,the displacement input model instead of acceleration model is usually adopted for accurate results.In this paper,a more detailed and comprehensive analysis of the displacement input model is carried out and the research shows that there exists an unnegligible problem in the current displacement model,which leads to the irrationality and unconvergence of some calculated results such as base shear etc.Based on the situation,an effective method named massless rigid element(MRE)method is presented to solve the problem.Moreover,the rationality and accuracy of the method are further assessed and the method is applied to a transmission tower-line system project using the commercially available structural analysis software SAP2000.The theoretical and numerical analyses indicate that the MRE approach is not only feasible with sufficient computational accuracy but also practical and can be easily implemented using the commercially available finite element software such as SAP2000.展开更多
Covalent organic frameworks(COFs)are an emerging class of porous crystalline materials formed by the precise assembly of organic molecular building blocks into extended periodic structures via strong covalent bonds.Th...Covalent organic frameworks(COFs)are an emerging class of porous crystalline materials formed by the precise assembly of organic molecular building blocks into extended periodic structures via strong covalent bonds.They feature well-defined pore structure,high specific surface area,and tunable physicochemical properties,endowing them with broad application prospects in gas storage,molecular separation.展开更多
Polyoxometalate-based metal–organic frameworks(POM-based MOFs)are extended structures that simultaneously possess the virtues of POMs and MOFs.They have been attracting immense attention because of their diverse arch...Polyoxometalate-based metal–organic frameworks(POM-based MOFs)are extended structures that simultaneously possess the virtues of POMs and MOFs.They have been attracting immense attention because of their diverse architectures and charming topologies,and also due to their probable application prospects in the areas of catalysis,sorption and separation,magnetism,proton conduction,lithium-ion batteries,supercapacitors,electrochemistry,medicine,and so on.In particular,the strong acidity,multielectron redox and photoactivity of POMs combined with the high surface area and adjustable pore size of MOFs make them excellent heterogeneous catalysts in various kinds of organic reactions.This short review firstly presents a concise introduction related to POMs,MOFs and POM-based MOFs,followed by the synthetic strategies of POM-based MOFs.The structural features and catalysis properties of representative POM-based MOFs have been classified and summarized according to different catalytic reactions,including acidity,oxidation,photocatalysis,electrocatalysis and other types of catalysis.The challenges present research situations,and prospects for the preparation and catalytic properties of POM-based MOFs are discussed.展开更多
The evaluation of N’-(1-(2-pyridyl)ethylidene)nicotinohydrazide(HL)as a linker for the Pb^(II)tagged extended structures is described.The reaction of Pb(ClO_(4))_(2)or Pb(OAc)_(2)with HL in MeOH at 60℃and room tempe...The evaluation of N’-(1-(2-pyridyl)ethylidene)nicotinohydrazide(HL)as a linker for the Pb^(II)tagged extended structures is described.The reaction of Pb(ClO_(4))_(2)or Pb(OAc)_(2)with HL in MeOH at 60℃and room temperature,respectively,leads to heteroleptic complexes{[PbL]ClO_(4)}n·nH_(2)O and[PbL(OAc)]_(2),while the same reaction of Pb(ClO_(4))_(2)with HL at 60℃in the presence of two equivalents of NaOAc or NaNO_(2)leads to heteroleptic complexes{[Pb(HL)(OAc)]ClO_(4)}_(n)and[PbL(NO_(2))]n,respectively.Using Pb(NO_(3))_(2)as a source of Pb^(II)in the same reaction with HL and two equivalents of NaN_(3)or NaNCS at room temperature yields[PbLN_(3)]_(n)and[Pb_(2)(HL)_(2)(NO_(3))_(2)(NCS)_(2)],respectively.The room temperature reaction of Pb(NO_(3))_(2)with HL in the presence of two equivalents of NaClO_(4)leads to the transformation of the parent ligand to its perchlorate salt[H_(2)L]ClO_(4).In all the obtained Pb^(II)structures,HL or its deprotonated form L acts both as a chelating and a bridging ligand.The nature of the inorganic anion also influences the final structure.In all complexes the Pb^(II)center exhibits a hemidirected coordination geometry with all the covalent bonds being concentrated on one hemisphere of the coordination sphere with the closest approach of two atoms on the other side varying from 151°to 232°.The sterically available Pb^(II)ion participates in tetrel bonding as evidenced from the detailed structural analysis of the described complexes.As a result of tetrel bonding,the structures of all the six compounds can be extended to a higher dimensional framework,which is further stabilized byπ…πstacking interactions between the aromatic rings.The DFT based charge and energy decomposition(ETS-NOCV)calculations are performed in order to shed light on the nature of non-covalent interactions that determine the stability of the obtained structures.展开更多
The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex s...The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex systems with the desired multifunctionality.Herein,we apply multi-edge X-ray absorption spectroscopy(extended X-ray absorption fine structure(EXAFS),Xray absorption near edge structure(XANES),and X-ray magnetic circular dichroism(XMCD))to probe the structural,electronic,and magnetic properties of all individual constituents in the single-phase face-centered cubic(fcc)-structured nanocrystalline thin film of Cr_(20)Mn_(26)Fe_(18)Co_(19)Ni_(17)(at.%)high-entropy alloy on the local scale.The local crystallographic ordering and componentdependent lattice displacements were explored within the reverse Monte Carlo approach applied to EXAFS spectra collected at the K absorption edges of several constituents at room temperature.A homogeneous short-range fcc atomic environment around the absorbers of each type with very similar statistically averaged interatomic distances(2.54-2.55Å)to their nearest-neighbors and enlarged structural relaxations of Cr atoms were revealed.XANES and XMCD spectra collected at the L2,3 absorption edges of all principal components at low temperature from the oxidized and in situ cleaned surfaces were used to probe the oxidation states,the changes in the electronic structure,and magnetic behavior of all constituents at the surface and in the sub-surface volume of the film.The spin and orbital magnetic moments of Fe,Co,and Ni components were quantitatively evaluated.The presence of magnetic phase transitions and the co-existence of different magnetic phases were uncovered by conventional magnetometry in a broad temperature range.展开更多
Gel'fand-Dorfman bialgebra,which is both a Lie algebra and a Novikov algebra with some compatibility condition,appeared in the study of Hamiltonian pairs in completely integrable systems.They also emerged in the d...Gel'fand-Dorfman bialgebra,which is both a Lie algebra and a Novikov algebra with some compatibility condition,appeared in the study of Hamiltonian pairs in completely integrable systems.They also emerged in the description of a class special Lie conformal algebras called quadratic Lie conformal algebras.In this paper,we investigate the extending structures problem for Gel'fand-Dorfman bialgebras,which is equivalent to some extending structures problem of quadratic Lie conformal algebras.Explicitly,given a Gel'fand-Dorfman bialgebra(A,o,[.,.]),this problem is how to describe and classify all Gel'fand-Dorfman bialgebra structures on a vector space E(A⊂E)such that(A,o,[.,.])is a subalgebra of E up to an isomorphism whose restriction on A is the identity map.Motivated by the theories of extending structures for Lie algebras and Novikov algebras,we construct an object gH2(V,A)to answer the extending structures problem by introducing the notion of a unified product for Gel'fand-Dorfman bialgebras,where V is a complement of A in E.In particular,we investigate the special case when dim(V)=1 in detail.展开更多
Negative thermal expansion(NTE)has both scientific and application value as a novel physical behavior,but the types of NTE materials are still limited.In the present work,a framework structure material,metal dicyanami...Negative thermal expansion(NTE)has both scientific and application value as a novel physical behavior,but the types of NTE materials are still limited.In the present work,a framework structure material,metal dicyanamide Zn[N(CN)_(2)]_(2),has been found to show biaxial negative thermal expansion in a wide temperature range(α_(a)=−11.82×10^(−6)K^(−1),α_(b)=−11.75×10^(−6)K^(−1)from 173 K–473 K).Through a joint study of variable temperature X-ray diffraction,extended X-ray absorption fine structure,Raman spectroscopy,and the maximum entropy method,the NTE mechanisms in Zn[N(CN)_(2)]_(2)have been revealed.The pronounced transverse vibration of C atoms in the multiatomic bridge linkage–N≡C–N–and the rotation of ZnN_(4)tetrahedra play a key role in biaxial negative thermal expansion.This work provides a new class of potential framework structure NTE materials.展开更多
In our study,the composition-dependent effects of atomic displacementsin Au-Cu-Ni-Pd-Pt basedalloys,comprising elements with large differences in atomic radii,are investigated at the atomic scale.Two alloys-the equimo...In our study,the composition-dependent effects of atomic displacementsin Au-Cu-Ni-Pd-Pt basedalloys,comprising elements with large differences in atomic radii,are investigated at the atomic scale.Two alloys-the equimolar AuCuNiPdPt and AuCuNiPd-have been characterized using multi-edge extended X-ray absorption fine structure(EXAFS)spectroscopy in conjunction with reverse Monte Carlo(RMC)simulations at room temperature.The statistically-averaged component-dependent pair distribution functions(PDFs),which represent the distribution of atoms around the assumed regular face-centered cubic(fcc)lattice positions,reveal a shift of their peaks to shorter distances and a pronounced asymmetry in atomic distribution only for atoms with small radi(Cu/Ni).The analysis demonstrates that small atoms(Cu/Ni)are significantly more displaced from the expected lattice positions as compared to large atoms(Au/Pt).Furthermore,there are indications of preferential next-neighbour bonding that changes depending on the alloy composition.The most pronounced changes in the PDFs were found solely for Pd.With this study,we provide a basis for a deeper understanding of the composition-dependent atomic arrangement in chemically complex solid solutions.展开更多
The effects of pH,contact time and natural organic ligands on radionuclide Eu(Ⅲ) adsorption and mechanism on titanate nanotubes(TNTs) are studied by a combination of batch and extended X-ray absorption fine structure...The effects of pH,contact time and natural organic ligands on radionuclide Eu(Ⅲ) adsorption and mechanism on titanate nanotubes(TNTs) are studied by a combination of batch and extended X-ray absorption fine structure(EXAFS) techniques.Macroscopic measurements show that the adsorption is ionic strength dependent at pH < 6.0,but ionic strength independent at pH > 6.0.The presence of humic acid(HA) /fulvic acid(FA) increases Eu(Ⅲ) adsorption on TNTs at low pH,but reduces Eu(Ⅲ) adsorption at high pH.The results of EXAFS analysis indicate that Eu(Ⅲ) adsorption on TNTs is dominated by outer-sphere surface complexation at pH < 6.0,whereas by inner-sphere surface complexation at pH > 6.0.At pH < 6.0,Eu(Ⅲ) consists of ～ 9 O atoms at REu?O ≈ 2.40 in the first coordination sphere,and a decrease in NEu-O with increasing pH indicates the introduction of more asymmetry in the first sphere of adsorbed Eu(Ⅲ).At long contact time or high pH values,the Eu(Ⅲ) consists of ～2 Eu at REu-Eu ≈ 3.60 and ～ 1 Ti at REu-Ti ≈ 4.40 ,indicating the formation of inner-sphere surface complexation,surface precipitation or surface polymers.Surface adsorbed HA/FA on TNTs modifies the species of adsorbed Eu(Ⅲ) as well as the local atomic structures of adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids.Adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids forms both ligand-bridging ternary surface complexes(Eu-HA/FA-TNTs) as well as surface complexes in which Eu(Ⅲ) remains directly bound to TNT surface hydroxyl groups(i.e.,binary Eu-TNTs or Eu-bridging ternary surface complexes(HA/FA-Eu-TNTs)).The findings in this work are important to describe Eu(Ⅲ) interaction with nanomaterials at molecular level and will help to improve the understanding of Eu(Ⅲ) physicochemical behavior in the natural environment.展开更多
The local environment of Cu atoms in Fe73.5Cu1Nb3Si13.5B9 alloy was investigated by extended X-ray absorption fine structure(EXAFS).Cu clusters began to order when the annealing temperature was around 733 K from the r...The local environment of Cu atoms in Fe73.5Cu1Nb3Si13.5B9 alloy was investigated by extended X-ray absorption fine structure(EXAFS).Cu clusters began to order when the annealing temperature was around 733 K from the results of the Fourier transform curves.The fitting results showed that the first shell of the near fcc(face-centered cubic)Cu clusters only contained Cu atoms.The coordination number increased with the annealing temperature.Subsequently,the occupancy rate increased from 33.3%(annealed at 733 K)to 100% (annealed at 853 K).This local structural change of Cu atoms could probably affect the distribution of the bcc(body-centered cubic)α-Fe in Fe73.5Cu1Nb3Si13.5B9 alloy.展开更多
基金Supported by:National Science Fund for Distinguished Young Scholars of China Under Grant No. 50425824the National Natural Science Foundation of China Under Grant No.50578109,90715034 and 90715032
文摘In the field of civil engineering, magnetorheological fluid （MRF） damper-based semi-active control systems have received considerable attention for use in protecting structures from natural hazards such as strong earthquakes and high winds. In this paper, the MRF damper-based semi-active control system is applied to a long-span spatially extended structure and its feasibility is discussed. Meanwhile, a _trust-region method based instantaneous optimal semi-active control algorithm （TIOC） is proposed to improve the performance of the semi-active control system in a multiple damper situation. The proposed TIOC describes the control process as a bounded constraint optimization problem, in which an optimal semi- active control force vector is solved by the trust-region method in every control step to minimize the structural responses. A numerical example of a railway station roof structure installed with MRF-04K dampers is presented. First, a modified Bouc- Wen model is utilized to describe the behavior of the selected MRF-04K damper. Then, two semi-active control systems, including the well-known clipped-optimal controller and the proposed TIOC controller, are considered. Based on the characteristics of the long-span spatially extended structure, the performance of the control system is evaluated under uniform earthquake excitation and travelling-wave excitation with different apparent velocities. The simulation results indicate that the MR fluid damper-based semi-active control systems have the potential to mitigate the responses of full-scale long-span spatially extended structures under earthquake hazards. The superiority of the proposed TIOC controller is demonstrated by comparing its control effectiveness with the clipped-optimal controller for several different cases.
基金supported by the National Natural Science Foundation of China(Grant No.11975307).
文摘Accurate identification of influential nodes facilitates the control of rumor propagation and interrupts the spread of computer viruses.Many classical approaches have been proposed by researchers regarding different aspects.To explore the impact of location information in depth,this paper proposes an improved global structure model to characterize the influence of nodes.The method considers both the node’s self-information and the role of the location information of neighboring nodes.First,degree centrality of each node is calculated,and then degree value of each node is used to represent self-influence,and degree values of the neighbor layer nodes are divided by the power of the path length,which is path attenuation used to represent global influence.Finally,an extended improved global structure model that considers the nearest neighbor information after combining self-influence and global influence is proposed to identify influential nodes.In this paper,the propagation process of a real network is obtained by simulation with the SIR model,and the effectiveness of the proposed method is verified from two aspects of discrimination and accuracy.The experimental results show that the proposed method is more accurate in identifying influential nodes than other comparative methods with multiple networks.
基金supported by the(NRF)grants funded by the Ministry of Science,the ICT Future Planning(MSIP)of Korea under NRF-2016M3D1A1027663,NRF-2016M3D1A1027664(Future Materials Discovery Program),and NRF-2021R1A3B1076723(Research Leader Program)。
文摘Perovskite solar cells (PSCs) employing formamidinium lead iodide (FAPbI_(3)) have shown high efficiency.However,operational stability has been issued due to phase instability of α phase FAPbI_(3) at ambient temperature.Excess precursors in the perovskite precursor solution has been proposed to improve not only power conversion efficiency (PCE) but also device stability.Nevertheless,there is a controversial issue on the beneficial effect on PCE and/or stability between excess FAI and excess PbI_(2).We report here extended X-ray absorption fine structure (EXAFS) of FAPbI_(3) to study local structural change and explain the effect of excess precursors on photovoltaic performance and stability.Perovskite films prepared from the precursor solution with excess PbI_(2)shows better stability than those from the one with excess FAI,despite similar PCE.A rapid phase transition from α phase to non-perovskite δ phase is observed from the perovskite film formed by excess FAI.Furthermore,the (Pb-I) bond distance evaluated by the Pb L_(III)-edge EXAFS study is increased by excess FAI,which is responsible for the phase transition and poor device stability.This work can provide important insight into local structure-stability relation in the FAPbI_(3)-based PSCs.
基金supported by the Postdoctoral station Foundation of Ministry of Education(No.20060200002)the Testing Foundation of Northeast Normal University
文摘A new 3D extended structural compound, （dpdo）2H2{[Cu（2,2＇-bipy）212（P2W18O62）}.SH2O 1 （dpdo = 4,4＇-bipyridine-N,N＇- dioxide; 2,2＇-bipy = 2,2＇-bipyridine）, has been hydrothermally synthesized and characterized by elemental analyses, IR, TG analyses, cyclic voltammetry, and single-crystal X-my diffraction. Compound 1 is built up of [P2WlsO62]6- cluster as the structural motif covalently linked by [Cu（2,2＇-bipy）2]^2＋ coordination complexes to yield the 1D chains, which axe further in close contact forming a 3D supramolecular framework via aromatic π-π stacking interactions and extensive hydrogen-bonding interactions among polyoxoanions, coordinated 2,2＇-bipy organic ligands, free dpdo organic molecules and lattice water molecules.
基金supported by the National Natural Science Foundation of China(No.51073111)
文摘Thin wall samples of high density polyethylene （HDPE） were prepared via injection molding with different injection speeds ranging from 100 mm/s to 1200 mm/s. A significant decrease in the tensile strength and Young＇s modulus was observed with increasing injection speed. In order to investigate the mechanism behind this decrease, the orientation, molecular weight, molecular weight distribution, melt flow rate, crystallinity and crystal morphology of HDPE were characterized using two-dimensional wide-angle X-ray diffraction （2D-WAXD）, gel permeation chromatography （GPC）, capillary rheometry and differential scanning calorimetry （DSC）, respectively. It is demonstrated that the orientation, molecular weight, molecular weight distribution, melt flow rate and crystallinity have no obvious change with increasing injection speed. Nevertheless, the content of extended chain crystals or large folded chain crystals was found to decrease with increasing injection speed. Therefore, it is concluded that the decrease in tensile properties is mainly contributed by the reduced content of extended chain crystals or large folded chain crystals. This study provides industry with valuable information for the application of high speed injection molding.
文摘Effect of structure parameter n and its coupling with the connection mode among RuO6 octahedra of Srn＋1RUnO3n＋1 （n = 1, 2, ∞） are investigated. The gradually enhanced rotation and tilting effect with increasing n are observed in Srn＋1RUnO3n＋1. Besides, the chemical valence of Ru is not changed, while the one of Sr gradually varies with increasing n, which highlights the great contribution of connection mode to the chemical environment. Our results show a strong n dependence on the connection mode between octahedra in Srn＋1RUnO3n＋1 （n = 1, 2, ∞）.
基金supported by the National Natural Science Foundation of China(22209155 and 52201283)China Postdoctoral Science Foundation(2024M752941,2022TQ0291,and 2022M712869)+1 种基金Henan Postdoctoral Science Foundation(HN2024059)Frontier Exploration Projects of Longmen Laboratory(LMQYTSKT021).
文摘Lithium-sulfur(Li-S)batteries hold great promise for the next generation of high energy density systems.However,sluggish sulfur conversion and the shuttle effect of polysulfides severely limit their commercial applications.Herein,a multifunctional covalent organic framework(Ni-COF)with extendedπ-d conjugated structure was synthesized and used for separator modification to overcome the obstacles in Li-S batteries.Ni-COF inherits the advantages of both COFs and conductive metal-organic frameworks,while compensating for their respective disadvantages.The abundant oxygen-containing groups in Ni-COF act as chemical adsorption sites to inhibit the shuttle effect of polysulfides.The designedπ-d conjugated structure enhances electrical conductivity and provides high-density metal catalytic sites,thereby facilitating the conversion of polysulfides and enhancing the reaction kinetics of Li-S batteries.Consequently,the Li-S batteries with Ni-COF@PP separator exhibit remarkable rate performance of 719 mA h g^(-1)at 4 C,along with a low attenuation rate of 0.087%per cycle over 300 cycles at 1 C.This study proposes a novel strategy for the rational design of COFs in Li-S batteries.
文摘Synchrotron radiation extended X-ray absorption fine structure(SR EXAFS)was used to study the transformation of coordination and redox state of arsenic(As)in a newly discovered As hyperaccumulator,Pteris vittata L.,which is considered to have great potential for phytoremediating the As contaminated soil.It is shown that the As in this plant was mainly coordinated with oxygen in thereduced state,As(IIl),and the reduction of As(V)occurred in the root after it was taken up.No oxidationof As(II)was found during the translocation of As,from root to shoot.Only a small amount of As was coordinated with sulfur in root and petiole,but not distinct in pinna.
基金supported by UT-INSA Program(2013)the support of the China Scholarship Council(CSC)
文摘Airframe maintenance is traditionally performed at scheduled maintenance stops.The decision to repair a fuselage panel is based on a fixed crack size threshold,which allows to ensure the aircraft safety until the next scheduled maintenance stop.With progress in sensor technology and data processing techniques,structural health monitoring（SHM） systems are increasingly being considered in the aviation industry.SHM systems track the aircraft health state continuously,leading to the possibility of planning maintenance based on an actual state of aircraft rather than on a fixed schedule.This paper builds upon a model-based prognostics framework that the authors developed in their previous work,which couples the Extended Kalman filter（EKF） with a firstorder perturbation（FOP） method.By using the information given by this prognostics method,a novel cost driven predictive maintenance（CDPM） policy is proposed,which ensures the aircraft safety while minimizing the maintenance cost.The proposed policy is formally derived based on the trade-off between probabilities of occurrence of scheduled and unscheduled maintenance.A numerical case study simulating the maintenance process of an entire fleet of aircrafts is implemented.Under the condition of assuring the same safety level,the CDPM is compared in terms of cost with two other maintenance policies：scheduled maintenance and threshold based SHM maintenance.The comparison results show CDPM could lead to significant cost savings.
基金Funded by the National Natural Science Foundation of China(No.51178114)the Fundamental Research Funds for the Central Universities(No.CXLX12_0117)the Scientifi c Research Foundation of Graduate School of Southeast University(No.YBJJ1318)
文摘The distributed optical fiber sensing technology was used to investigate the fracture behavior of the Epoxy Asphalt Mixture. The spatial distribution and variation of the strain development with crack propagation were acquired using the brillouin optical time-domain reflectometer through the loading experiments of the composite beam structure. In addition, a finite element model of the composite beam structure was developed to analyze the mechanical responses of the epoxy asphalt mixture using the extended finite element method. The experimental results show that the development of crack propagation becomes instable with the increase of the load, and larger loads will generate deeper cracks. Moreover, the numerical results show that the mechanical response of the crack tip changes with the crack propagation, and the worst areas that subjected to crack damage are located on both sides of the composite beam structure.
基金supported by the Scientific Research Foundation of Central South Universitythe National Natural Science Foundation of China(Grant No.50638010)the Foundation of Ministry of Education for Innovation Group(Grant No.IRT0518)
文摘In the seismic analysis of extended structures subject to spatially varying motions,the displacement input model instead of acceleration model is usually adopted for accurate results.In this paper,a more detailed and comprehensive analysis of the displacement input model is carried out and the research shows that there exists an unnegligible problem in the current displacement model,which leads to the irrationality and unconvergence of some calculated results such as base shear etc.Based on the situation,an effective method named massless rigid element(MRE)method is presented to solve the problem.Moreover,the rationality and accuracy of the method are further assessed and the method is applied to a transmission tower-line system project using the commercially available structural analysis software SAP2000.The theoretical and numerical analyses indicate that the MRE approach is not only feasible with sufficient computational accuracy but also practical and can be easily implemented using the commercially available finite element software such as SAP2000.
文摘Covalent organic frameworks(COFs)are an emerging class of porous crystalline materials formed by the precise assembly of organic molecular building blocks into extended periodic structures via strong covalent bonds.They feature well-defined pore structure,high specific surface area,and tunable physicochemical properties,endowing them with broad application prospects in gas storage,molecular separation.
基金supported by the National Natural Science Foundation of China(21601058 and 21771112)111 project(B12015)the Hunan Provincial Natural Science Foundation of China(2018JJ3146).
文摘Polyoxometalate-based metal–organic frameworks(POM-based MOFs)are extended structures that simultaneously possess the virtues of POMs and MOFs.They have been attracting immense attention because of their diverse architectures and charming topologies,and also due to their probable application prospects in the areas of catalysis,sorption and separation,magnetism,proton conduction,lithium-ion batteries,supercapacitors,electrochemistry,medicine,and so on.In particular,the strong acidity,multielectron redox and photoactivity of POMs combined with the high surface area and adjustable pore size of MOFs make them excellent heterogeneous catalysts in various kinds of organic reactions.This short review firstly presents a concise introduction related to POMs,MOFs and POM-based MOFs,followed by the synthetic strategies of POM-based MOFs.The structural features and catalysis properties of representative POM-based MOFs have been classified and summarized according to different catalytic reactions,including acidity,oxidation,photocatalysis,electrocatalysis and other types of catalysis.The challenges present research situations,and prospects for the preparation and catalytic properties of POM-based MOFs are discussed.
基金the PL-Grid Infrastructure and resources provided by the ACC Cyfronet AGH(Cracow,Poland).
文摘The evaluation of N’-(1-(2-pyridyl)ethylidene)nicotinohydrazide(HL)as a linker for the Pb^(II)tagged extended structures is described.The reaction of Pb(ClO_(4))_(2)or Pb(OAc)_(2)with HL in MeOH at 60℃and room temperature,respectively,leads to heteroleptic complexes{[PbL]ClO_(4)}n·nH_(2)O and[PbL(OAc)]_(2),while the same reaction of Pb(ClO_(4))_(2)with HL at 60℃in the presence of two equivalents of NaOAc or NaNO_(2)leads to heteroleptic complexes{[Pb(HL)(OAc)]ClO_(4)}_(n)and[PbL(NO_(2))]n,respectively.Using Pb(NO_(3))_(2)as a source of Pb^(II)in the same reaction with HL and two equivalents of NaN_(3)or NaNCS at room temperature yields[PbLN_(3)]_(n)and[Pb_(2)(HL)_(2)(NO_(3))_(2)(NCS)_(2)],respectively.The room temperature reaction of Pb(NO_(3))_(2)with HL in the presence of two equivalents of NaClO_(4)leads to the transformation of the parent ligand to its perchlorate salt[H_(2)L]ClO_(4).In all the obtained Pb^(II)structures,HL or its deprotonated form L acts both as a chelating and a bridging ligand.The nature of the inorganic anion also influences the final structure.In all complexes the Pb^(II)center exhibits a hemidirected coordination geometry with all the covalent bonds being concentrated on one hemisphere of the coordination sphere with the closest approach of two atoms on the other side varying from 151°to 232°.The sterically available Pb^(II)ion participates in tetrel bonding as evidenced from the detailed structural analysis of the described complexes.As a result of tetrel bonding,the structures of all the six compounds can be extended to a higher dimensional framework,which is further stabilized byπ…πstacking interactions between the aromatic rings.The DFT based charge and energy decomposition(ETS-NOCV)calculations are performed in order to shed light on the nature of non-covalent interactions that determine the stability of the obtained structures.
文摘The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex systems with the desired multifunctionality.Herein,we apply multi-edge X-ray absorption spectroscopy(extended X-ray absorption fine structure(EXAFS),Xray absorption near edge structure(XANES),and X-ray magnetic circular dichroism(XMCD))to probe the structural,electronic,and magnetic properties of all individual constituents in the single-phase face-centered cubic(fcc)-structured nanocrystalline thin film of Cr_(20)Mn_(26)Fe_(18)Co_(19)Ni_(17)(at.%)high-entropy alloy on the local scale.The local crystallographic ordering and componentdependent lattice displacements were explored within the reverse Monte Carlo approach applied to EXAFS spectra collected at the K absorption edges of several constituents at room temperature.A homogeneous short-range fcc atomic environment around the absorbers of each type with very similar statistically averaged interatomic distances(2.54-2.55Å)to their nearest-neighbors and enlarged structural relaxations of Cr atoms were revealed.XANES and XMCD spectra collected at the L2,3 absorption edges of all principal components at low temperature from the oxidized and in situ cleaned surfaces were used to probe the oxidation states,the changes in the electronic structure,and magnetic behavior of all constituents at the surface and in the sub-surface volume of the film.The spin and orbital magnetic moments of Fe,Co,and Ni components were quantitatively evaluated.The presence of magnetic phase transitions and the co-existence of different magnetic phases were uncovered by conventional magnetometry in a broad temperature range.
基金Supported by the National Natural Science Foundation of China(Grant Nos.12171129,11871421)the Zhejiang Provincial Natural Science Foundation of China(Grant No.LY20A010022)the Scientific Research Foundation of Hangzhou Normal University(Grant No.2019QDL012)。
文摘Gel'fand-Dorfman bialgebra,which is both a Lie algebra and a Novikov algebra with some compatibility condition,appeared in the study of Hamiltonian pairs in completely integrable systems.They also emerged in the description of a class special Lie conformal algebras called quadratic Lie conformal algebras.In this paper,we investigate the extending structures problem for Gel'fand-Dorfman bialgebras,which is equivalent to some extending structures problem of quadratic Lie conformal algebras.Explicitly,given a Gel'fand-Dorfman bialgebra(A,o,[.,.]),this problem is how to describe and classify all Gel'fand-Dorfman bialgebra structures on a vector space E(A⊂E)such that(A,o,[.,.])is a subalgebra of E up to an isomorphism whose restriction on A is the identity map.Motivated by the theories of extending structures for Lie algebras and Novikov algebras,we construct an object gH2(V,A)to answer the extending structures problem by introducing the notion of a unified product for Gel'fand-Dorfman bialgebras,where V is a complement of A in E.In particular,we investigate the special case when dim(V)=1 in detail.
基金supported by the National Natural Science Foundation of China(Grant No.22101020,12104038,and 21825102)the Fundamental Research Funds for the Central Universities,China(06500201 and No.FRF-TP-20-041A2)+1 种基金the ELETTRA Synchrotron Trieste for provision of synchrotron radiation(Experiment No.20210156)the staff of the XAFS Beamline for technical assistance.
文摘Negative thermal expansion(NTE)has both scientific and application value as a novel physical behavior,but the types of NTE materials are still limited.In the present work,a framework structure material,metal dicyanamide Zn[N(CN)_(2)]_(2),has been found to show biaxial negative thermal expansion in a wide temperature range(α_(a)=−11.82×10^(−6)K^(−1),α_(b)=−11.75×10^(−6)K^(−1)from 173 K–473 K).Through a joint study of variable temperature X-ray diffraction,extended X-ray absorption fine structure,Raman spectroscopy,and the maximum entropy method,the NTE mechanisms in Zn[N(CN)_(2)]_(2)have been revealed.The pronounced transverse vibration of C atoms in the multiatomic bridge linkage–N≡C–N–and the rotation of ZnN_(4)tetrahedra play a key role in biaxial negative thermal expansion.This work provides a new class of potential framework structure NTE materials.
文摘In our study,the composition-dependent effects of atomic displacementsin Au-Cu-Ni-Pd-Pt basedalloys,comprising elements with large differences in atomic radii,are investigated at the atomic scale.Two alloys-the equimolar AuCuNiPdPt and AuCuNiPd-have been characterized using multi-edge extended X-ray absorption fine structure(EXAFS)spectroscopy in conjunction with reverse Monte Carlo(RMC)simulations at room temperature.The statistically-averaged component-dependent pair distribution functions(PDFs),which represent the distribution of atoms around the assumed regular face-centered cubic(fcc)lattice positions,reveal a shift of their peaks to shorter distances and a pronounced asymmetry in atomic distribution only for atoms with small radi(Cu/Ni).The analysis demonstrates that small atoms(Cu/Ni)are significantly more displaced from the expected lattice positions as compared to large atoms(Au/Pt).Furthermore,there are indications of preferential next-neighbour bonding that changes depending on the alloy composition.The most pronounced changes in the PDFs were found solely for Pd.With this study,we provide a basis for a deeper understanding of the composition-dependent atomic arrangement in chemically complex solid solutions.
基金supported by the National Natural Science Foundation of China(20907055,20971126 & 21077107)the National Basic Research Program of China(2007CB936602 & 2011CB933700)
文摘The effects of pH,contact time and natural organic ligands on radionuclide Eu(Ⅲ) adsorption and mechanism on titanate nanotubes(TNTs) are studied by a combination of batch and extended X-ray absorption fine structure(EXAFS) techniques.Macroscopic measurements show that the adsorption is ionic strength dependent at pH < 6.0,but ionic strength independent at pH > 6.0.The presence of humic acid(HA) /fulvic acid(FA) increases Eu(Ⅲ) adsorption on TNTs at low pH,but reduces Eu(Ⅲ) adsorption at high pH.The results of EXAFS analysis indicate that Eu(Ⅲ) adsorption on TNTs is dominated by outer-sphere surface complexation at pH < 6.0,whereas by inner-sphere surface complexation at pH > 6.0.At pH < 6.0,Eu(Ⅲ) consists of ～ 9 O atoms at REu?O ≈ 2.40 in the first coordination sphere,and a decrease in NEu-O with increasing pH indicates the introduction of more asymmetry in the first sphere of adsorbed Eu(Ⅲ).At long contact time or high pH values,the Eu(Ⅲ) consists of ～2 Eu at REu-Eu ≈ 3.60 and ～ 1 Ti at REu-Ti ≈ 4.40 ,indicating the formation of inner-sphere surface complexation,surface precipitation or surface polymers.Surface adsorbed HA/FA on TNTs modifies the species of adsorbed Eu(Ⅲ) as well as the local atomic structures of adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids.Adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids forms both ligand-bridging ternary surface complexes(Eu-HA/FA-TNTs) as well as surface complexes in which Eu(Ⅲ) remains directly bound to TNT surface hydroxyl groups(i.e.,binary Eu-TNTs or Eu-bridging ternary surface complexes(HA/FA-Eu-TNTs)).The findings in this work are important to describe Eu(Ⅲ) interaction with nanomaterials at molecular level and will help to improve the understanding of Eu(Ⅲ) physicochemical behavior in the natural environment.
基金supported by the National Natural Science Foundation of China(Grant No.51071109)the Young Excellent Talents in Tongji University(Grant No.2009KJ003)
文摘The local environment of Cu atoms in Fe73.5Cu1Nb3Si13.5B9 alloy was investigated by extended X-ray absorption fine structure(EXAFS).Cu clusters began to order when the annealing temperature was around 733 K from the results of the Fourier transform curves.The fitting results showed that the first shell of the near fcc(face-centered cubic)Cu clusters only contained Cu atoms.The coordination number increased with the annealing temperature.Subsequently,the occupancy rate increased from 33.3%(annealed at 733 K)to 100% (annealed at 853 K).This local structural change of Cu atoms could probably affect the distribution of the bcc(body-centered cubic)α-Fe in Fe73.5Cu1Nb3Si13.5B9 alloy.
