Establishing the structure-property relationship in amorphous materials has been a long-term grand challenge due to the lack of a unified description of the degree of disorder.In this work,we develop SPRamNet,a neural...Establishing the structure-property relationship in amorphous materials has been a long-term grand challenge due to the lack of a unified description of the degree of disorder.In this work,we develop SPRamNet,a neural network based machine-learning pipeline that effectively predicts structure-property relationship of amorphous material via global descriptors.Applying SPRamNet on the recently discovered amorphous monolayer carbon,we successfully predict the thermal and electronic properties.More importantly,we reveal that a short range of pair correlation function can readily encode sufficiently rich information of the structure of amorphous material.Utilizing powerful machine learning architectures,the encoded information can be decoded to reconstruct macroscopic properties involving many-body and long-range interactions.Establishing this hidden relationship offers a unified description of the degree of disorder and eliminates the heavy burden of measuring atomic structure,opening a new avenue in studying amorphous materials.展开更多
The deformation work rate can be expressed by the time rate of pair functional potentials which describe the energy of materi- als in terms of atomic bonds and atom embedding interactions. According to Cauchy-Born rul...The deformation work rate can be expressed by the time rate of pair functional potentials which describe the energy of materi- als in terms of atomic bonds and atom embedding interactions. According to Cauchy-Born rule, the relations between the micro- scopic deformations of atomic bonds and electron gas and macroscopic deformation are established. Further, atomic bonds are grouped according to their directions, and atomic bonds in the same direction are simplified as a spring-bundle component. Atom embedding interactions in unit reference volume are simplified as a cubage component. Consequently, a material model com- posed of spring-bundle components and a cubage component is established. Since the essence of damage is the decrease and loss of atomic bonding forces, the damage effect can be reflected by the response functions of these two kinds of components. For- mulating the mechanical responses of two kinds of components, the corresponding elasto-damage constitutive equations are de- rived. Considering that slip is the main plastic deformation mechanism of polycrystalline metals, the slip systems of crystal are extended to polycrystalline, and the slip components are proposed to describe the plastic deformation. Based on the decomposition of deformation gradient and combining the plastic response with the elasto-damage one, the elasto-plastic damage constitutive equations are derived. As a result, a material model iormulated with spring-bundle components, a cubage component and slip components is established. Different from phenomenological constitutive theories, the mechanical property of materials depends on the property of components rather than that directly obtained on the representative volume element. The effect of finite deformation is taken into account in this model. Parameter calibration procedure and the basic characteristics of this model are discussed.展开更多
The atomic pair distribution function（PDF） reveals the interatomic distance in a material directly in real-space. It is a very powerful method to characterize the local structure of materials. With the help of the t...The atomic pair distribution function（PDF） reveals the interatomic distance in a material directly in real-space. It is a very powerful method to characterize the local structure of materials. With the help of the third generation synchrotron facility and spallation neutron source worldwide, the PDF method has developed quickly both experimentally and theoretically in recent years. Recently this method was successfully implemented at the Shanghai Synchrotron Radiation Facility（SSRF）. The data quality is very high and this ensures the applicability of the method to study the subtle structural changes in complex materials. In this article, we introduce in detail this new method and show some experimental data we collected.展开更多
The study of minus paired domination of a graph G=(V,E) is initiated. Let SV be any paired dominating set of G , a minus paired dominating function is a function of the form f∶V→{-1,0,1} such that ...The study of minus paired domination of a graph G=(V,E) is initiated. Let SV be any paired dominating set of G , a minus paired dominating function is a function of the form f∶V→{-1,0,1} such that f(v)= 1 for v∈S, f(v)≤0 for v∈V-S , and f(N)≥1 for all v∈V . The weight of a minus paired dominating function f is w(f)=∑f(v) , over all vertices v∈V . The minus paired domination number of a graph G is γ - p( G )=min{ w(f)|f is a minus paired dominating function of G }. On the basis of the minus paired domination number of a graph G defined, some of its properties are discussed.展开更多
The structure transitions in cluster-cluster aggregation (CCA) and diffusion-limited aggregation (DLA) under external electric fields have been investigated by computer simulations. With the increase of external elect...The structure transitions in cluster-cluster aggregation (CCA) and diffusion-limited aggregation (DLA) under external electric fields have been investigated by computer simulations. With the increase of external electric field, there exists a structure transition from disorder to order, i. e., the aggregates change from fractals of diffusion-limited CCA and DLA to the electrorheological chains parallel to electric field. Pair distribution shows, the system changes from local order to long-range order gradually with the external field rising.展开更多
We used interpretable machine learning to combine information from multiple heterogeneous spectra:X-ray absorption near-edge spectra(XANES)and atomic pair distribution functions(PDFs)to extract local structural and ch...We used interpretable machine learning to combine information from multiple heterogeneous spectra:X-ray absorption near-edge spectra(XANES)and atomic pair distribution functions(PDFs)to extract local structural and chemical environments of transition metal cations in oxides.Random forest models were trained on simulated XANES,PDF,and both combined to extract oxidation state,coordination number,and mean nearest-neighbor bond length.XANES-only models generally outperformed PDF-only models,even for structural tasks,although using the metal’s differential-PDFs(dPDFs)instead of total-PDFs narrowed this gap.When combined with PDFs,information from XANES often dominates the prediction.Our results demonstrate that XANES contains rich structural information and highlight the utility of species-specificity.This interpretable,multimodal approach is quick to implement with suitable databases and offers valuable insights into the relative strengths of different modalities,guiding researchers in experiment design and identifying when combining complementary techniques adds meaningful information to a scientific investigation.展开更多
A new model for self-diffusion coefficients was proposed based oil both the concepts of molecular free volume and activation energy. The unknown parameters of this model were clearly defined and compared with the Chap...A new model for self-diffusion coefficients was proposed based oil both the concepts of molecular free volume and activation energy. The unknown parameters of this model were clearly defined and compared with the Chapman-Enskog model. At the same time a new method for calculating activation energy was devised and applied to the new model. In addition, the free volume was defined by implementing the generic van der Waals equation of state, the radial distribution function of which was obtained by using the Morsali- Goharshadi empirical formula. Under the same conditions, the new model was better than the original free volume model.展开更多
Metal-organic frameworks(MOFs),a family of highly porous materials possessing huge surface areas and feasible chemical tunability,are emerging as critical functional materials to solve the growing challenges associate...Metal-organic frameworks(MOFs),a family of highly porous materials possessing huge surface areas and feasible chemical tunability,are emerging as critical functional materials to solve the growing challenges associated with energy-water systems,such as water scarcity issues.In this contribution,the roles of MOFs are highlighted in electrochemical-based water applications(i.e.,reactions,sensing,and separations),where MOF-based functional materials exhibit outstanding performances in detecting/removing pollutants,recovering resources,and harvesting energies from different water sources.Compared with the pristine MOFs,the efficiency and/or selectivity can be further enhanced via rational structural modulation of MOFs(e.g.,partial metal substitution)or integration of MOFs with other functional materials(e.g.,metal clusters and reduced graphene oxide).Several key factors/properties that affect the performances of MOF-based materials are also reviewed,including electronic structures,nanoconfined effects,stability,conductivity,and atomic structures.The advancement in the fundamental understanding of these key factors is expected to shed light on the functioning mechanisms of MOFs(e.g.,charge transfer pathways and vip-host interactions),which will subsequently accelerate the integration of precisely designed MOFs into electrochemical architectures to achieve highly effective water remediation with optimized selectivity and long-term stability.展开更多
The increased use of rechargeable batteries in portable electronic devices and the continuous develop-ment of novel applications （e.g. transportation and large scale energy storage）, have raised a strong de-mand for...The increased use of rechargeable batteries in portable electronic devices and the continuous develop-ment of novel applications （e.g. transportation and large scale energy storage）, have raised a strong de-mand for high performance batteries with increased energy density, cycle and calendar life, safety andlower costs. This triggers significant efforts to reveal the fundamental mechanism determining batteryperformance with the use of advanced analytical techniques. However, the inherently complex character-istics of battery systems make the mechanism analysis sophisticated and difficult. Synchrotron radiationis an advanced collimated light source with high intensity and tunable energies. It has particular ad-vantages in electronic structure and geometric structure （both the short-range and long-range structure）analysis of materials on different length and time scales. In the past decades, synchrotron X-ray tech-niques have been widely used to understand the fundamental mechanism and guide the technologicaloptimization of batteries. In particular, in situ and operando techniques with high spatial and temporalresolution, enable the nondestructive, real time dynamic investigation of the electrochemical reaction,and lead to significant deep insights into the battery operation mechanism. This review gives a brief introduction of the application of synchrotron X-ray techniques to the inves-tigation of battery systems. The five widely implicated techniques, including X-ray diffraction （XRD）, PairDistribution Function （PDF）, Hard and Soft X-ray absorption spectroscopy （XAS） and X-ray photoelectronspectroscopy （XPS） will be reviewed, with the emphasis on their in situ studies of battery systems during cycling.展开更多
A kind of amphiphilic functional monomer was selected to modify polyacrylamide （PAM） or partially hydrolyzed polyacrylamide （HPAM）. The relative properties of the modified polyacrylamide （HM-PAM） and modified pa...A kind of amphiphilic functional monomer was selected to modify polyacrylamide （PAM） or partially hydrolyzed polyacrylamide （HPAM）. The relative properties of the modified polyacrylamide （HM-PAM） and modified partially hydrolyzed polyacrylamide （HM-HPAM） such as radius of gyration （Rg）, hydrodynamic radius （RH）, and radial distribution functions （RDFs） have been studied to find the intrinsic relation between the microstructure of the polymer chain and the intrinsic viscosities with changing the amotmt of modified monomers from 1% to 4%. The simulation results show that, compared to HPAM, HM-HPAM has a better performance in increasing viscosity when the percentage of modified monomers is 2% and has a stronger salt tolerance when the modified monomers is 4%. Furthermore, a complex hydrogen bonding network was revealed with the analysis of radial distribution functions （RDFs） and the pair correlation function was used to investigate the diffusivity of Na^＋ and carbon atoms in the COO^- group.展开更多
It has been demonstrated that intermolecular interaction,crucial in a plenty of chemical and physical processes,may vary in the presence of metal surface.However,such modification is yet to be quantitatively revealed....It has been demonstrated that intermolecular interaction,crucial in a plenty of chemical and physical processes,may vary in the presence of metal surface.However,such modification is yet to be quantitatively revealed.Here,we present a systematical density functional theory study on adsorbed bis（para-pyridyl）acetylene（BPPA） tetramer on Au（111） surface.We observed unusually high electron density between two head-to-head N atoms,an intermolecular ＂non-bonded＂ region,in adsorbed BPPA tetramer.This exceptional electron density originates from the wavefunction hybridization of the two compressed N lone-electron-pair states of two BPPA,as squeezed by a newly revealed N-Au-N threecenter bonding.This bond,together with the minor contribution from N...H-C intermolecular hydrogen bonding,shortens the N-N distance from over 4 A to 3.30 A and offers an attractive lateral interacting energy of 0.60 eV,effectively to a surface-confined in-plane pressure.The overlapped non-bonding vvavefunction hybridization arising from the effective pressure induced by the N-Au-N three-center bonding,as not been fully recognized in earlier studies,was manifested in non-contact Atomic Force Microscopy.展开更多
A well-established pseodopotential is used to study the structure of some 4f rare earth liquid metals （Ce, Pr, Eu, Gd, Tb, and Yb）. The structure factor S（q）, pair distribution function g（r）, interatomic distanc...A well-established pseodopotential is used to study the structure of some 4f rare earth liquid metals （Ce, Pr, Eu, Gd, Tb, and Yb）. The structure factor S（q）, pair distribution function g（r）, interatomic distance r1, and coordination number n1 are calculated using Charged Hard Sphere （CHS） reference system. To introduce the exchange and correlation effects, the local field correction due to Sarkar et al. （S） is applied. The present investigation is successful in generating the structural information of Ce, Pr, Eu, Gd, Tb, and Yb 4f rare earth liquid metals.展开更多
The energy materials performance is intrinsically determined by structures from the average lattice structure to the atom arrangement, valence, and distribution of the containing transition metal(TM) elements. Underst...The energy materials performance is intrinsically determined by structures from the average lattice structure to the atom arrangement, valence, and distribution of the containing transition metal(TM) elements. Understanding the mechanism of the structure transition and atom rearrangement via synthesis or processing is key to expediting the exploration of excellent energy materials. In this work, in situ neutron scattering is employed to reveal the real-time structure evolution, including the TM-O bonds, lattice,TM valence and the migration of the high-voltage spinel cathode LiNi_(0.5)Mn_(1.5)O_(4). The transition-metalmediated spinel destabilization under the annealing at the oxygen-deficient atmosphere is pinpointed.The formation of Mn^(3+) is correlated to the TM migration activation, TM disordered rearrangement in the spinel, and the transition to a layered-rocksalt phase. The further TM interdiffusion and Mn^(3+) reduction are also revealed with multi-stage thermodynamics and kinetics. The mechanisms of phase transition and atom migrations as functions of temperature, time and atmosphere present important guidance on the synthesis in various-valence element containing oxides.展开更多
In mathematics, space encompasses various structured sets such as Euclidean, metric, or vector space. This article introduces temporal space—a novel concept independent of traditional spatial dimensions and frames of...In mathematics, space encompasses various structured sets such as Euclidean, metric, or vector space. This article introduces temporal space—a novel concept independent of traditional spatial dimensions and frames of reference, accommodating multiple object-oriented durations in a dynamical system. The novelty of building temporal space using finite geometry is rooted in recent advancements in the theory of relationalism which utilizes Euclidean geometry, set theory, dimensional analysis, and a causal signal system. Multiple independent and co-existing cyclic durations are measurable as a network of finite one-dimensional timelines. The work aligns with Leibniz’s comments on relational measures of duration with the addition of using discrete cyclic relational events that define these finite temporal spaces, applicable to quantum and classical physics. Ancient formulas have symmetry along with divisional and subdivisional orders of operations that create discrete and ordered temporal geometric elements. Elements have cyclically conserved symmetry but unique cyclic dimensional quantities applicable for anchoring temporal equivalence relations in linear time. We present both fixed equivalences and expanded periods of temporal space offering a non-Greek calendar methodology consistent with ancient global timekeeping descriptions. Novel applications of Euclid’s division algorithm and Cantor’s pairing function introduce a novel paired function equation. The mathematical description of finite temporal space within relationalism theory offers an alternative discrete geometric methodology for examining ancient timekeeping with new hypotheses for Egyptian calendars.展开更多
The mechanism research of structure-related reactions on Li_2MnO_3 is important to enhance the electrochemical performance of lithium-manganese-rich layered oxides.Although there are some reports on the structure evol...The mechanism research of structure-related reactions on Li_2MnO_3 is important to enhance the electrochemical performance of lithium-manganese-rich layered oxides.Although there are some reports on the structure evolution of Li_2MnO_3 during cycling process,the employed research techniques are very limited,mainly in/ex-situ X-ray diffraction,X-ray absorption and transmission electron microscopy.Here,atomic pair distribution function,a method to study the local atomic arrangement on the basis of average spectroscopic information,is used for the first time to study the local structure evolution of Li_2MnO_3 during electrochemical charge/discharge cycles.The results clearly demonstrate that Mn^(3+)/Mn^(4+)redox couple is activated and Mn ions are reduced during discharging process.Some Mn ions in Mn layers can significantly migrate to Li layers and occupy the octahedral sites.As a result,a portion of inserted Li ions can occupy the face-shared tetrahedron sites,accompanied by the formation of local spinel-like structure.This work provides an important and suitable method based on the average spectroscopic information to investigate the local structure of electrode materials of lithium-ion batteries as well as other advanced battery systems.展开更多
Zeolite-supported noble metal nanoparticle(NP)catalysts demonstrate distinctive properties in heterogeneous catalysis reactions.However,due to the limitations of conventional liquid-phase synthesis methods,understandi...Zeolite-supported noble metal nanoparticle(NP)catalysts demonstrate distinctive properties in heterogeneous catalysis reactions.However,due to the limitations of conventional liquid-phase synthesis methods,understanding of the dynamic crystallization mechanism of zeolites on the microscopic scale is still limited.Importantly,it impedes the in-depth establishment of relationship between structure and reactivity.Herein,we successfully develop a unique solvent-free and organic template-free solid-phase synthesis strategy for preparing Pt/ZSM-5 encapsulated structures to investigate the time-resolved dynamic evolution of zeolite crystallization process.Using the time-resolved X-ray atom pair distribution function and the in-situ scanning electron microscopy technique,the“dissolution-recrystallization”transformation mechanism of structural evolution for zeolite is observed.This dynamic mechanism induces AlO_(4)structural distortion in Pt/ZSM-5 encapsulated structure,triggering strong metal-support interaction.The enhancement of Brønsted acid density and the cationic of Pt mediates the process of cracking of C–C bonds and hydrogenation of C=C bonds.Pt NPs confined in mesoporous pores of ZSM-5 improve the mass transfer efficiency of reaction intermediates.Therefore,Pt/ZSM-5 exhibits remarkable polyethylene hydrocracking performance,achieving approximately 90%conversion and higher liquid fuel selectivity.The complementary analysis of multimodal spectroscopy and in-situ imaging techniques advance our fundamental understanding of structure-activity relationships in zeolite-supported noble metal NPs catalysts.展开更多
The design of stabilizing controllers for general nonlinear systems remains a challenging task due to their inherent complexities and nonconvexities.In this paper,we consider the problem of designing an asymptotically...The design of stabilizing controllers for general nonlinear systems remains a challenging task due to their inherent complexities and nonconvexities.In this paper,we consider the problem of designing an asymptotically stable controller of a nonlinear dynamic system.We begin by framing the problem as an inverse optimal control problem,aiming to design a pair of cost functions that ensure asymptotic stability for the nonlinear model predictive control closed-loop system.By leveraging the relaxed dynamic programming inequality,a machine learning based algorithm is proposed to learn the cost functions.Finally,we demonstrate the effectiveness of the proposed method through illustrative examples.展开更多
A new method to calculate mutual-diffusion coefficients of the binary alloy has been proposed in this report.At first self-diffusion coefficient of the constituent element was calculated using molecular dynamics metho...A new method to calculate mutual-diffusion coefficients of the binary alloy has been proposed in this report.At first self-diffusion coefficient of the constituent element was calculated using molecular dynamics method,thermodynamic factor of the alloy was got with the NRTL(non-random-two-liquid)equation,then mutual-diffusion coefficient was obtained with Darken formula.Using this method the mutual-diffusion coefficient of Pb-Mg alloy with different Pb content was calculated.The calculated values were compared with the available experimental ones and the reason of the maximal mutual-diffusion coefficient appearing at 33.3 at.%Pb was discussed.Partial pair correlation function and partial coordination number were calculated to analyze the effect of the melt structure on mutual-diffusion coefficient.展开更多
Under different temperatures and concentrations, the diffusion of Vitamin C （VC） in water solution was exam- ined by molecular dynamics simulation. The diffusion coefficients were calculated based on the Einstein eq...Under different temperatures and concentrations, the diffusion of Vitamin C （VC） in water solution was exam- ined by molecular dynamics simulation. The diffusion coefficients were calculated based on the Einstein equation. The influences of temperature, concentration, and simulation time on the diffusion coefficient were discussed. The results showed that at higher temperature and lower concentration the normal diffusions appear relatively late, but the linear range of mean square displacement curves continues longer than that at lower temperature and higher concentration. At the same temperature, the normal diffusion time increases and the diffusion coefficient decreases as the simulation concentration increases. These simulation results are in good agreement with experiments. Analyses of the pair correlation functions of the simulation systems showed that hydrogen bonds are mainly formed be- tween the hydrogen atoms of VC molecules and oxygen atoms of H20 molecules, rather than between the O atoms of VC molecules and H atoms of H20 molecules. The diffusion coefficient is higher as the interaction between water molecules and VC molecules is stronger when VC concentration is lower. The water in the model systems affects the diffusion of VC molecules by the short-range repulsion of O（H20）-O（H20） pairs and the non-bond interaction of H（H20）-H（H20） pairs. The short-range repulsion of O（H20）-O（H20） pairs is greater when VC concentration is higher, the diffusion of VC is weaker. The greater the non-bond interaction of H（H20）-H（H20） pairs is, the higher the VC diffusion is. It is expected that this study can provide a theoretical direction for the experiments on the mass transfer of VC in water solution.展开更多
基金supported by the National Key R&D Program of China under Grant No.2021YFA1400500the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No.XDB33000000+1 种基金the National Natural Science Foundation of China under Grant No.12334003the Beijing Municipal Natural Science Foundation under Grant Nos.JQ22001 and QY23014。
文摘Establishing the structure-property relationship in amorphous materials has been a long-term grand challenge due to the lack of a unified description of the degree of disorder.In this work,we develop SPRamNet,a neural network based machine-learning pipeline that effectively predicts structure-property relationship of amorphous material via global descriptors.Applying SPRamNet on the recently discovered amorphous monolayer carbon,we successfully predict the thermal and electronic properties.More importantly,we reveal that a short range of pair correlation function can readily encode sufficiently rich information of the structure of amorphous material.Utilizing powerful machine learning architectures,the encoded information can be decoded to reconstruct macroscopic properties involving many-body and long-range interactions.Establishing this hidden relationship offers a unified description of the degree of disorder and eliminates the heavy burden of measuring atomic structure,opening a new avenue in studying amorphous materials.
基金National Natural Science Foundation of China (10572140,10721202)
文摘The deformation work rate can be expressed by the time rate of pair functional potentials which describe the energy of materi- als in terms of atomic bonds and atom embedding interactions. According to Cauchy-Born rule, the relations between the micro- scopic deformations of atomic bonds and electron gas and macroscopic deformation are established. Further, atomic bonds are grouped according to their directions, and atomic bonds in the same direction are simplified as a spring-bundle component. Atom embedding interactions in unit reference volume are simplified as a cubage component. Consequently, a material model com- posed of spring-bundle components and a cubage component is established. Since the essence of damage is the decrease and loss of atomic bonding forces, the damage effect can be reflected by the response functions of these two kinds of components. For- mulating the mechanical responses of two kinds of components, the corresponding elasto-damage constitutive equations are de- rived. Considering that slip is the main plastic deformation mechanism of polycrystalline metals, the slip systems of crystal are extended to polycrystalline, and the slip components are proposed to describe the plastic deformation. Based on the decomposition of deformation gradient and combining the plastic response with the elasto-damage one, the elasto-plastic damage constitutive equations are derived. As a result, a material model iormulated with spring-bundle components, a cubage component and slip components is established. Different from phenomenological constitutive theories, the mechanical property of materials depends on the property of components rather than that directly obtained on the representative volume element. The effect of finite deformation is taken into account in this model. Parameter calibration procedure and the basic characteristics of this model are discussed.
基金Project supported by the National Natural Science Foundation of China(Grant No.U1232112)the National Key Basic Research Program of China(Grant No.2012CB825700)
文摘The atomic pair distribution function（PDF） reveals the interatomic distance in a material directly in real-space. It is a very powerful method to characterize the local structure of materials. With the help of the third generation synchrotron facility and spallation neutron source worldwide, the PDF method has developed quickly both experimentally and theoretically in recent years. Recently this method was successfully implemented at the Shanghai Synchrotron Radiation Facility（SSRF）. The data quality is very high and this ensures the applicability of the method to study the subtle structural changes in complex materials. In this article, we introduce in detail this new method and show some experimental data we collected.
文摘The study of minus paired domination of a graph G=(V,E) is initiated. Let SV be any paired dominating set of G , a minus paired dominating function is a function of the form f∶V→{-1,0,1} such that f(v)= 1 for v∈S, f(v)≤0 for v∈V-S , and f(N)≥1 for all v∈V . The weight of a minus paired dominating function f is w(f)=∑f(v) , over all vertices v∈V . The minus paired domination number of a graph G is γ - p( G )=min{ w(f)|f is a minus paired dominating function of G }. On the basis of the minus paired domination number of a graph G defined, some of its properties are discussed.
文摘The structure transitions in cluster-cluster aggregation (CCA) and diffusion-limited aggregation (DLA) under external electric fields have been investigated by computer simulations. With the increase of external electric field, there exists a structure transition from disorder to order, i. e., the aggregates change from fractals of diffusion-limited CCA and DLA to the electrorheological chains parallel to electric field. Pair distribution shows, the system changes from local order to long-range order gradually with the external field rising.
基金funded by Toyota Research Institute,grant number PO-002332.
文摘We used interpretable machine learning to combine information from multiple heterogeneous spectra:X-ray absorption near-edge spectra(XANES)and atomic pair distribution functions(PDFs)to extract local structural and chemical environments of transition metal cations in oxides.Random forest models were trained on simulated XANES,PDF,and both combined to extract oxidation state,coordination number,and mean nearest-neighbor bond length.XANES-only models generally outperformed PDF-only models,even for structural tasks,although using the metal’s differential-PDFs(dPDFs)instead of total-PDFs narrowed this gap.When combined with PDFs,information from XANES often dominates the prediction.Our results demonstrate that XANES contains rich structural information and highlight the utility of species-specificity.This interpretable,multimodal approach is quick to implement with suitable databases and offers valuable insights into the relative strengths of different modalities,guiding researchers in experiment design and identifying when combining complementary techniques adds meaningful information to a scientific investigation.
文摘A new model for self-diffusion coefficients was proposed based oil both the concepts of molecular free volume and activation energy. The unknown parameters of this model were clearly defined and compared with the Chapman-Enskog model. At the same time a new method for calculating activation energy was devised and applied to the new model. In addition, the free volume was defined by implementing the generic van der Waals equation of state, the radial distribution function of which was obtained by using the Morsali- Goharshadi empirical formula. Under the same conditions, the new model was better than the original free volume model.
基金supported by the start-up package and COES Institutional Research Incentive Program at the Florida Institute of Technology.
文摘Metal-organic frameworks(MOFs),a family of highly porous materials possessing huge surface areas and feasible chemical tunability,are emerging as critical functional materials to solve the growing challenges associated with energy-water systems,such as water scarcity issues.In this contribution,the roles of MOFs are highlighted in electrochemical-based water applications(i.e.,reactions,sensing,and separations),where MOF-based functional materials exhibit outstanding performances in detecting/removing pollutants,recovering resources,and harvesting energies from different water sources.Compared with the pristine MOFs,the efficiency and/or selectivity can be further enhanced via rational structural modulation of MOFs(e.g.,partial metal substitution)or integration of MOFs with other functional materials(e.g.,metal clusters and reduced graphene oxide).Several key factors/properties that affect the performances of MOF-based materials are also reviewed,including electronic structures,nanoconfined effects,stability,conductivity,and atomic structures.The advancement in the fundamental understanding of these key factors is expected to shed light on the functioning mechanisms of MOFs(e.g.,charge transfer pathways and vip-host interactions),which will subsequently accelerate the integration of precisely designed MOFs into electrochemical architectures to achieve highly effective water remediation with optimized selectivity and long-term stability.
基金the National Natural Science Foundation of China (Grant nos.21233004,21303147 and 21473148,etc.)the National Key Research and Development Program (Grant no.2016YFB0901500)
文摘The increased use of rechargeable batteries in portable electronic devices and the continuous develop-ment of novel applications （e.g. transportation and large scale energy storage）, have raised a strong de-mand for high performance batteries with increased energy density, cycle and calendar life, safety andlower costs. This triggers significant efforts to reveal the fundamental mechanism determining batteryperformance with the use of advanced analytical techniques. However, the inherently complex character-istics of battery systems make the mechanism analysis sophisticated and difficult. Synchrotron radiationis an advanced collimated light source with high intensity and tunable energies. It has particular ad-vantages in electronic structure and geometric structure （both the short-range and long-range structure）analysis of materials on different length and time scales. In the past decades, synchrotron X-ray tech-niques have been widely used to understand the fundamental mechanism and guide the technologicaloptimization of batteries. In particular, in situ and operando techniques with high spatial and temporalresolution, enable the nondestructive, real time dynamic investigation of the electrochemical reaction,and lead to significant deep insights into the battery operation mechanism. This review gives a brief introduction of the application of synchrotron X-ray techniques to the inves-tigation of battery systems. The five widely implicated techniques, including X-ray diffraction （XRD）, PairDistribution Function （PDF）, Hard and Soft X-ray absorption spectroscopy （XAS） and X-ray photoelectronspectroscopy （XPS） will be reviewed, with the emphasis on their in situ studies of battery systems during cycling.
基金financially supported by the National Natural Science Foundation of China(No.20904035)
文摘A kind of amphiphilic functional monomer was selected to modify polyacrylamide （PAM） or partially hydrolyzed polyacrylamide （HPAM）. The relative properties of the modified polyacrylamide （HM-PAM） and modified partially hydrolyzed polyacrylamide （HM-HPAM） such as radius of gyration （Rg）, hydrodynamic radius （RH）, and radial distribution functions （RDFs） have been studied to find the intrinsic relation between the microstructure of the polymer chain and the intrinsic viscosities with changing the amotmt of modified monomers from 1% to 4%. The simulation results show that, compared to HPAM, HM-HPAM has a better performance in increasing viscosity when the percentage of modified monomers is 2% and has a stronger salt tolerance when the modified monomers is 4%. Furthermore, a complex hydrogen bonding network was revealed with the analysis of radial distribution functions （RDFs） and the pair correlation function was used to investigate the diffusivity of Na^＋ and carbon atoms in the COO^- group.
基金supported by the Ministry of Science and Technology(MOST)of China(Nos.2012CB932704,2012CB933001)the National Natural Science Foundation of China(NSFC,Nos.11274380,91433103,21173058,11622437,61674171 and 21203038)supported by the Outstanding Innovative Talents Cultivation Funded Programs 2015 of Renmin University of China
文摘It has been demonstrated that intermolecular interaction,crucial in a plenty of chemical and physical processes,may vary in the presence of metal surface.However,such modification is yet to be quantitatively revealed.Here,we present a systematical density functional theory study on adsorbed bis（para-pyridyl）acetylene（BPPA） tetramer on Au（111） surface.We observed unusually high electron density between two head-to-head N atoms,an intermolecular ＂non-bonded＂ region,in adsorbed BPPA tetramer.This exceptional electron density originates from the wavefunction hybridization of the two compressed N lone-electron-pair states of two BPPA,as squeezed by a newly revealed N-Au-N threecenter bonding.This bond,together with the minor contribution from N...H-C intermolecular hydrogen bonding,shortens the N-N distance from over 4 A to 3.30 A and offers an attractive lateral interacting energy of 0.60 eV,effectively to a surface-confined in-plane pressure.The overlapped non-bonding vvavefunction hybridization arising from the effective pressure induced by the N-Au-N three-center bonding,as not been fully recognized in earlier studies,was manifested in non-contact Atomic Force Microscopy.
基金The project supported by University Grants Commission, New Delhi, India
文摘A well-established pseodopotential is used to study the structure of some 4f rare earth liquid metals （Ce, Pr, Eu, Gd, Tb, and Yb）. The structure factor S（q）, pair distribution function g（r）, interatomic distance r1, and coordination number n1 are calculated using Charged Hard Sphere （CHS） reference system. To introduce the exchange and correlation effects, the local field correction due to Sarkar et al. （S） is applied. The present investigation is successful in generating the structural information of Ce, Pr, Eu, Gd, Tb, and Yb 4f rare earth liquid metals.
基金supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy (DOE)。
文摘The energy materials performance is intrinsically determined by structures from the average lattice structure to the atom arrangement, valence, and distribution of the containing transition metal(TM) elements. Understanding the mechanism of the structure transition and atom rearrangement via synthesis or processing is key to expediting the exploration of excellent energy materials. In this work, in situ neutron scattering is employed to reveal the real-time structure evolution, including the TM-O bonds, lattice,TM valence and the migration of the high-voltage spinel cathode LiNi_(0.5)Mn_(1.5)O_(4). The transition-metalmediated spinel destabilization under the annealing at the oxygen-deficient atmosphere is pinpointed.The formation of Mn^(3+) is correlated to the TM migration activation, TM disordered rearrangement in the spinel, and the transition to a layered-rocksalt phase. The further TM interdiffusion and Mn^(3+) reduction are also revealed with multi-stage thermodynamics and kinetics. The mechanisms of phase transition and atom migrations as functions of temperature, time and atmosphere present important guidance on the synthesis in various-valence element containing oxides.
文摘In mathematics, space encompasses various structured sets such as Euclidean, metric, or vector space. This article introduces temporal space—a novel concept independent of traditional spatial dimensions and frames of reference, accommodating multiple object-oriented durations in a dynamical system. The novelty of building temporal space using finite geometry is rooted in recent advancements in the theory of relationalism which utilizes Euclidean geometry, set theory, dimensional analysis, and a causal signal system. Multiple independent and co-existing cyclic durations are measurable as a network of finite one-dimensional timelines. The work aligns with Leibniz’s comments on relational measures of duration with the addition of using discrete cyclic relational events that define these finite temporal spaces, applicable to quantum and classical physics. Ancient formulas have symmetry along with divisional and subdivisional orders of operations that create discrete and ordered temporal geometric elements. Elements have cyclically conserved symmetry but unique cyclic dimensional quantities applicable for anchoring temporal equivalence relations in linear time. We present both fixed equivalences and expanded periods of temporal space offering a non-Greek calendar methodology consistent with ancient global timekeeping descriptions. Novel applications of Euclid’s division algorithm and Cantor’s pairing function introduce a novel paired function equation. The mathematical description of finite temporal space within relationalism theory offers an alternative discrete geometric methodology for examining ancient timekeeping with new hypotheses for Egyptian calendars.
基金supported financially by the Beijing Natural Science Foundation(B)(KZ201610005003)National Natural Science Foundation of China(51622202,U1507107,21603009 and 51802009)+1 种基金National Key R&D Program of China(2018YFB0104302)Guangdong Science and Technology Project(2016B010114001)
文摘The mechanism research of structure-related reactions on Li_2MnO_3 is important to enhance the electrochemical performance of lithium-manganese-rich layered oxides.Although there are some reports on the structure evolution of Li_2MnO_3 during cycling process,the employed research techniques are very limited,mainly in/ex-situ X-ray diffraction,X-ray absorption and transmission electron microscopy.Here,atomic pair distribution function,a method to study the local atomic arrangement on the basis of average spectroscopic information,is used for the first time to study the local structure evolution of Li_2MnO_3 during electrochemical charge/discharge cycles.The results clearly demonstrate that Mn^(3+)/Mn^(4+)redox couple is activated and Mn ions are reduced during discharging process.Some Mn ions in Mn layers can significantly migrate to Li layers and occupy the octahedral sites.As a result,a portion of inserted Li ions can occupy the face-shared tetrahedron sites,accompanied by the formation of local spinel-like structure.This work provides an important and suitable method based on the average spectroscopic information to investigate the local structure of electrode materials of lithium-ion batteries as well as other advanced battery systems.
基金the financial support provided by the National Natural Science Foundation of China(grant no.52161145403)the Iran National Science Foundation(grant no.4001399)the Research Fund of Shenyang National Laboratory for Materials Science.
文摘Zeolite-supported noble metal nanoparticle(NP)catalysts demonstrate distinctive properties in heterogeneous catalysis reactions.However,due to the limitations of conventional liquid-phase synthesis methods,understanding of the dynamic crystallization mechanism of zeolites on the microscopic scale is still limited.Importantly,it impedes the in-depth establishment of relationship between structure and reactivity.Herein,we successfully develop a unique solvent-free and organic template-free solid-phase synthesis strategy for preparing Pt/ZSM-5 encapsulated structures to investigate the time-resolved dynamic evolution of zeolite crystallization process.Using the time-resolved X-ray atom pair distribution function and the in-situ scanning electron microscopy technique,the“dissolution-recrystallization”transformation mechanism of structural evolution for zeolite is observed.This dynamic mechanism induces AlO_(4)structural distortion in Pt/ZSM-5 encapsulated structure,triggering strong metal-support interaction.The enhancement of Brønsted acid density and the cationic of Pt mediates the process of cracking of C–C bonds and hydrogenation of C=C bonds.Pt NPs confined in mesoporous pores of ZSM-5 improve the mass transfer efficiency of reaction intermediates.Therefore,Pt/ZSM-5 exhibits remarkable polyethylene hydrocracking performance,achieving approximately 90%conversion and higher liquid fuel selectivity.The complementary analysis of multimodal spectroscopy and in-situ imaging techniques advance our fundamental understanding of structure-activity relationships in zeolite-supported noble metal NPs catalysts.
文摘The design of stabilizing controllers for general nonlinear systems remains a challenging task due to their inherent complexities and nonconvexities.In this paper,we consider the problem of designing an asymptotically stable controller of a nonlinear dynamic system.We begin by framing the problem as an inverse optimal control problem,aiming to design a pair of cost functions that ensure asymptotic stability for the nonlinear model predictive control closed-loop system.By leveraging the relaxed dynamic programming inequality,a machine learning based algorithm is proposed to learn the cost functions.Finally,we demonstrate the effectiveness of the proposed method through illustrative examples.
基金supported by the National Natural Science Foundation of China-Yunnan United Foundation(Grant No.U0837604)
文摘A new method to calculate mutual-diffusion coefficients of the binary alloy has been proposed in this report.At first self-diffusion coefficient of the constituent element was calculated using molecular dynamics method,thermodynamic factor of the alloy was got with the NRTL(non-random-two-liquid)equation,then mutual-diffusion coefficient was obtained with Darken formula.Using this method the mutual-diffusion coefficient of Pb-Mg alloy with different Pb content was calculated.The calculated values were compared with the available experimental ones and the reason of the maximal mutual-diffusion coefficient appearing at 33.3 at.%Pb was discussed.Partial pair correlation function and partial coordination number were calculated to analyze the effect of the melt structure on mutual-diffusion coefficient.
基金This work was financially supported by open projectfrom the Key Laboratory of Genetic Breeding and Aquaculture Biology of Freshwater Fisher, Ministry of Agriculture, China （No. BZ2007-06） and the Natural Science Foundation of Jiangsu province, Higher Educa- tion Institution of China （No. 08KJD240003）.
文摘Under different temperatures and concentrations, the diffusion of Vitamin C （VC） in water solution was exam- ined by molecular dynamics simulation. The diffusion coefficients were calculated based on the Einstein equation. The influences of temperature, concentration, and simulation time on the diffusion coefficient were discussed. The results showed that at higher temperature and lower concentration the normal diffusions appear relatively late, but the linear range of mean square displacement curves continues longer than that at lower temperature and higher concentration. At the same temperature, the normal diffusion time increases and the diffusion coefficient decreases as the simulation concentration increases. These simulation results are in good agreement with experiments. Analyses of the pair correlation functions of the simulation systems showed that hydrogen bonds are mainly formed be- tween the hydrogen atoms of VC molecules and oxygen atoms of H20 molecules, rather than between the O atoms of VC molecules and H atoms of H20 molecules. The diffusion coefficient is higher as the interaction between water molecules and VC molecules is stronger when VC concentration is lower. The water in the model systems affects the diffusion of VC molecules by the short-range repulsion of O（H20）-O（H20） pairs and the non-bond interaction of H（H20）-H（H20） pairs. The short-range repulsion of O（H20）-O（H20） pairs is greater when VC concentration is higher, the diffusion of VC is weaker. The greater the non-bond interaction of H（H20）-H（H20） pairs is, the higher the VC diffusion is. It is expected that this study can provide a theoretical direction for the experiments on the mass transfer of VC in water solution.
