Regularized Boolean operations have been widely used in 3D modeling systems. However, evaluating Boolean operations may be quite numerically unstable and time consuming, especially for iterated set operations. A novel...Regularized Boolean operations have been widely used in 3D modeling systems. However, evaluating Boolean operations may be quite numerically unstable and time consuming, especially for iterated set operations. A novel and unified technique is proposed in this paper for computing single and iterated set operations efficiently, robustly and exactly. An adaptive octree is combined with a nested constructive solid geometry (CSG) tree by this technique. The intersection handling is restricted to the cells in the octree where intersection actually occurs. Within those cells, a CSG tree template is instanced by the surfaces and the tree is converted to planebased binary space partitioning (BSP) for set evaluation; Moreover, the surface classification is restricted to the ceils in the octree where the surfaces only come from a model and are within the bounding-boxes of other polyhedrons. These two ways bring about the efficiency and scalability of the operations, in terms of runtime and memory. As all surfaces in such a cell have the same classification relation, they are classified as a whole. Robustness and exactness are achieved by integrating plane-based geometry representation with adaptive geometry predicate technique in intersection handling, and by applying divide-and-conquer arithmetic on surface classification. Experimental results demonstrate that the proposed approach can guarantee the robustness of Boolean computations and runs faster than other existing approaches.展开更多
To improve the efficiency of oxygen electrolysis,exploiting bifunctional electrocatalysts with excellent activity and stability is extremely important due to the four-electron transfer dynamics of oxygen evolution rea...To improve the efficiency of oxygen electrolysis,exploiting bifunctional electrocatalysts with excellent activity and stability is extremely important due to the four-electron transfer dynamics of oxygen evolution reaction(OER)and oxygen reduction reaction(ORR).Herein,a series of yolk-shell hollow polyhedrons(YHPs)embedded with NiCoFe ternary alloy and metal oxides,which are named YHP-x(x=1,2,3,4),were reported.By controlled etching multi-layered zeolitic imidazolate frameworks and following pyrolytic integration,YHPs are endowed with mass transfer tunnels,accessible inner active sites,and good electrical conductivity.Due to the synergetic effect of the alloy,metal oxides and the yolk-shell structure,YHP-1 exhibits excellent ORR performance with a half-wave potential of 0.79 V and YHP-2 displays superior OER performance with a low overpotential of 257 mV at 10 mA cm−2.The strategy described in this work can be extended to a number of hollow/yolk-shell electrocatalysts for water splitting and metal–air batteries.展开更多
With the advantage of fast charge transfer,heterojunction engineering is identified as a viable method to reinforce the anodes'sodium storage performance.Also,vacancies can effectively strengthen the Na+adsorption...With the advantage of fast charge transfer,heterojunction engineering is identified as a viable method to reinforce the anodes'sodium storage performance.Also,vacancies can effectively strengthen the Na+adsorption ability and provide extra active sites for Na+adsorption.However,their synchronous engineering is rarely reported.Herein,a hybrid of Co_(0.85)Se/WSe_(2) heterostructure with Se vacancies and N-doped carbon polyhedron(CoWSe/NCP)has been fabricated for the first time via a hydrothermal and subsequent selenization strategy.Spherical aberration-corrected transmission electron microscopy confirms the phase interface of the Co_(0.85)Se/WSe_(2) heterostructure and the existence of Se vacancies.Density functional theory simulations reveal the accelerated charge transfer and enhanced Na+adsorption ability,which are contributed by the Co_(0.85)Se/WSe_(2) heterostructure and Se vacancies,respectively.As expected,the CoWSe/NCP anode in sodium-ion battery achieves outstanding rate capability(339.6 mAh g^(−1) at 20 A g^(−1)),outperforming almost all Co/W-based selenides.展开更多
Combining suitable microstructure and dielectric-magnetic synergy effect is conducive to achieve lightweight,broadband,and high-efficiency microwave absorbing materials within low filler loading.Herein,porous carbon p...Combining suitable microstructure and dielectric-magnetic synergy effect is conducive to achieve lightweight,broadband,and high-efficiency microwave absorbing materials within low filler loading.Herein,porous carbon polyhedrons coupled with bimetallic CoNi alloys were synthesized by using metalorganic frameworks(MOFs)as a template and subsequent pyrolysis treatment.Electromagnetic analysis indicated that the existence of metal Ni element could influence the wave attenuation capacity effectively,resulting in frequency selective wave absorption performance.Additionally,the pyrolysis temperature was also closely related to wave absorption intensity.The Co_(2)Ni_(1)/C/PVDF composites calcined at 800℃ possessed outstanding wave absorption performance at an ultra-low filler loading of 5 wt%.The minimum reflection loss value achieved-52 dB(10.8 GHz)under the matched thickness of 3 mm.Moreover,the broadest effective absorption bandwidth(RL<-10 dB)reached 6.2 dB(11.8-18 GHz)for Co/C-800/PVDF composites when the thickness turned into 2 mm.The remarkable wave attenuation ability was mainly ascribed to magnetic and dielectric loss,impedance matching as well as porous structure effect.展开更多
To gain insight into the structures and stability of F4F6 polyhedrons formed by squares and hexagons,a density functional theory study was performed on all isomers of F4F6 polyhedrons with sizes from 8 to 60.The calcu...To gain insight into the structures and stability of F4F6 polyhedrons formed by squares and hexagons,a density functional theory study was performed on all isomers of F4F6 polyhedrons with sizes from 8 to 60.The calculated results demonstrate that the six squares tend to isolate from each other,i.e.these F4F6 polyhedrons obey the isolated square rule.Those isomers with fewer B44 bonds(square-square adjacencies) are more stable than those with more B44 bonds,i.e.they obey square adjacency penalty rule.Both of the two rules in F4F6 polyhedrons are in the same status as the isolated pentagon rule and pentagon adjacency penalty rule in F5F6 fullerenes and can be used to screen the lowest energy isomers of F4F6 polyhedrons as IPR and PAPR do in classic fullerenes.Structural analysis demonstrates that the pyramidalization of carbon atoms at the square-square adjacencies determines the stability of corresponding structures.展开更多
Because of their large volume variation and inferior electrical conductivity,Mn_(3)O_(4)-based oxide anode materials have short cyclic lives and poor rate capability,which obstructs their development.In this study,we ...Because of their large volume variation and inferior electrical conductivity,Mn_(3)O_(4)-based oxide anode materials have short cyclic lives and poor rate capability,which obstructs their development.In this study,we successfully prepared a Mn_(3)O_(4)/N-doped honeycomb carbon composite using a smart and facile synthetic method.The Mn_(3)O_(4)nanopolyhedra are grown on N-doped honeycomb carbon,which evidently mitigates the volume change in the charging and discharging processes but also improves the electrochemical reaction kinetics.More importantly,the Mn-O-C bond in the Mn_(3)O_(4)/N-doped honeycomb carbon composite benefits electrochemical reversibility.These features of the Mn_(3)O_(4)/N-doped honeycomb carbon(NHC)composite are responsible for its superior electrochemical performance.When used for Li-ion batteries,the Mn_(3)O_(4)/N-doped honeycomb carbon anode exhibits a high reversible capacity of 598 mAh·g^(−1)after 350 cycles at 1 A·g^(−1).Even at 2 A·g^(−1),the Mn_(3)O_(4)/NHC anode still delivers a high capacity of 472 mAh·g^(−1).This work provides a new prospect for synthesizing and developing manganese-based oxide materials for energy storage.展开更多
It has been pointed out by the theoretic model of anion coordination polyhedra of growth units that the crystal form is dominated by the stability of combination of anion coordination polyhedra on the growth interface...It has been pointed out by the theoretic model of anion coordination polyhedra of growth units that the crystal form is dominated by the stability of combination of anion coordination polyhedra on the growth interface.The face has the fastest growth rate and disappears easily if the vertex of coordination polyhedron is pointed at.The face has the slowest growth rate and appears easily if the plane of coordination polyhedron is pointed at.The growth rate is in median for the face that the edge of coordination polyhedron is pointed at.A few of problems are discussed in the paper on the basis of this theory. (1)Several examples of the morphology of allomorph and homoeomorphism are given in the paper.There are three allomorphs of TiO 2 rutile,brookite and anatase.The morphology of these allomorphs are totally different because the stability of combination of octahedral [Ti O 6] 8- vary with the orientation and linked edges of coordination polyhedra.Another example is the homoeomorphism of cassiterite SnO 2.The orientation and combination of octahedral [Sn O 6] 8- in cassiterite are similar to that of octahedral [Ti O 6] 8- in rutile,so that cassiterite and rutile have similar morphology even for their form of twin and twin face.The combination of octahedral [Al O 6] 9- ,[Fe O 6] 9- and [Ti O 6] 8- respectively is similar at the orientation and linked form of coordination polyhedra in three crystals of corundum,hematite and ilmenite,so the same faces appear in these three crystals,resulted in similar morphology.展开更多
After undergoing wireframe modeling, surface modeling and solid modeling, a unified product model, which holds a variety of constraints in engineering, supports design process, and unifies the wire frame, surface mode...After undergoing wireframe modeling, surface modeling and solid modeling, a unified product model, which holds a variety of constraints in engineering, supports design process, and unifies the wire frame, surface modeling, and solid modeling,is a general tendency of modeling technology. A discussion is presented here on how tobuild a unified product model by using the complex method. The concept of complex inalgebraic topology is introduced into the model and a new B-REP representation of thenon-manifold model is given --Identification Edge Structure. Based on it, some basicoperators and high-level operators are built. The model has a rigorous mathematicalbasis, and is flexible and easy to extend, and holds the lamina face, lamina edge andlamina vertex. As a result, the variety of constraints in engineering, such as parametricconstraints, optimization methods, fuzzy constraints, artificial intelligent, etc., can beadded to the system. The model may form the kernel for the implementation of the nextgeneration CAD system --intelligent CAD system.展开更多
It is of significance to design of stable and cost-effective electrocatalyst for water splitting with high efficiency in an alkaline medium.The major obstacles for practical application of water splitting devices are ...It is of significance to design of stable and cost-effective electrocatalyst for water splitting with high efficiency in an alkaline medium.The major obstacles for practical application of water splitting devices are lack of high-efficiency and low-cost electrocatalysts with low overpotential for both HER and OER.In this paper,we report a NiFe alloy decorated NiCoO2 hollow polyhedron(denoted as Ni Fe–Ni Co O2)by using[NiFe(CN)6]- intercalated NiCo–LDH as precursor.As evidenced by the electrochemical active surface area,the resultant Ni Fe–Ni Co O2 composite shows unique hollow nanostructure,which can not only provide abundant mass transport channels,but also increase the contact area of the NiFe–Ni Co O2 material with the electrolyte.The overpotential(η)demand is 286 mV for OER and 102 mV for HER at the current density of 10 mA/cm2 in an alkaline medium of 1 M KOH for the NiFe/NiCoO2 composite.This work provides a new pathway for preparation of the highly efficient bifunctional electrocatalysts for water splitting.展开更多
The architecture of the Great Pyramid at Giza is based on fascinating golden mean geometry. Recently the ratio of the in-sphere volume to the pyramid volume was calculated. One yields as result <em>R</em>&...The architecture of the Great Pyramid at Giza is based on fascinating golden mean geometry. Recently the ratio of the in-sphere volume to the pyramid volume was calculated. One yields as result <em>R</em><sub><em>V</em></sub> = π <span style="white-space:nowrap;"><span style="white-space:nowrap;">⋅</span></span> <em><em style="white-space:normal;">φ</em></em><sup>5</sup>, where <img src="Edit_83decbce-7252-44ed-a822-fef13e43fd2a.bmp" alt="" /> is the golden mean. It is important that the number <em>φ</em><sup>5</sup> is a fundamental constant of nature describing phase transition from microscopic to cosmic scale. In this contribution the relatively small volume ratio of the Great Pyramid was compared to that of selected convex polyhedral solids such as the <em>Platonic </em>solids respectively the face-rich truncated icosahedron (bucky ball) as one of <em>Archimedes</em>’ solids leading to effective filling of the polyhedron by its in-sphere and therefore the highest volume ratio of the selected examples. The smallest ratio was found for the Great Pyramid. A regression analysis delivers the highly reliable volume ratio relation <img src="Edit_79e766ce-5580-4ae0-a706-570e0f3f1bd8.bmp" alt="" />, where <em>nF</em> represents the number of polyhedron faces and b approximates the silver mean. For less-symmetrical solids with a unique axis (tetragonal pyramids) the in-sphere can be replaced by a biaxial ellipsoid of maximum volume to adjust the <em>R</em><sub><em>V</em></sub> relation more reliably.展开更多
A new Koppelman-Leray-Norguet formula of (p,q) differential forms for a strictly pseudoconvex polyhedron with not necessarily smooth boundary on a Stein manifold is obtained, and an integral representation for the sol...A new Koppelman-Leray-Norguet formula of (p,q) differential forms for a strictly pseudoconvex polyhedron with not necessarily smooth boundary on a Stein manifold is obtained, and an integral representation for the solution of -equation on this domain which does not involve integrals on boundary is given, so one can avoid complex estimates of boundary integrals.展开更多
Freezing in ice rubble is a common phenomenon in cold regions,which can consolidate loose blocks and change their mechanical properties.To model the cohesive effect in frozen ice rubble,and to describe the fragmentati...Freezing in ice rubble is a common phenomenon in cold regions,which can consolidate loose blocks and change their mechanical properties.To model the cohesive effect in frozen ice rubble,and to describe the fragmentation behavior with a large external forces exerted,a freeze-bond model based on the dilated polyhedral discrete element method(DEM)is proposed.Herein,imaginary bonding is initialized at the contact points to transmit forces and moments,and the initiation of the damage is detected using the hybrid fracture model.The model is validated through the qualitative agreement between the simulation results and the analytical solution of two bonding particles.To study the effect of freeze-bond on the floating ice rubble,punch-through tests were simulated on the ice rubble under freezing and nonfreezing conditions.The deformation and resistance of the ice rubble are investigated during indenter penetration.The influence of the internal friction coefficient on the strength of the ice rubble is determined.The results indicate that the proposed model can properly describe the consolidated ice rubble,and the freeze-bond effect is of great significance to the ice rubble properties.展开更多
Shape modeling is fundamental to the analysis of dynamic environment and motion around asteroid. Chang'E- 2 successfully made a flyby of Asteroid 4179 Toutatis and obtained plenty of high-resolution images during the...Shape modeling is fundamental to the analysis of dynamic environment and motion around asteroid. Chang'E- 2 successfully made a flyby of Asteroid 4179 Toutatis and obtained plenty of high-resolution images during the mis- sion. In this paper, the modeling method and preliminary model of Asteroid Toutatis are discussed. First, the optical images obtained by Chang'E-2 are analyzed. Terrain and silhouette features in images are described. Then, the modeling method based on previous radar model and preliminary information from optical images is proposed. A preliminary polyhedron model of Asteroid Toutatis is established. Finally, the spherical harmonic coefficients of Asteroid Toutatis based on the polyhedron model are obtained. Some parameters of model are analyzed and compared. Although the model proposed in this paper is only a preliminary model, this work offers a valuable reference for future high-resolution models.展开更多
From the perspective of growth units, the growth mechanism of Mg2(OH)2CO3.3H2O whisker is investigated in this paper. Results show that the growth morphology of Mg2(OH)2CO33H2O whisker is consistent with the model...From the perspective of growth units, the growth mechanism of Mg2(OH)2CO3.3H2O whisker is investigated in this paper. Results show that the growth morphology of Mg2(OH)2CO33H2O whisker is consistent with the model of anion coordination polyhedron growth units. The growth solution Raman shift of Mg2(OH)2CO;3H2O was monitored using Raman spectroscopy. The growth units are [Mg-(OH)4]2- and H2COv The growth process of Mg2(OH)2COf3H2O whisker is as follows: growth unit [Mg-(OH)4]2- first incorporates into the larger dimension [Mg-(OH)4]2-, then the [Mg-(OH)4]2-n combines with H2CO3 into a linear skeleton Mg2(OH)2CO3 in the same line. Mg2(OH)2CO3 combines with H2O by hydrogen bonds and ultimately transforms into Mg2(OH)2COf3H2O whisker. Magnesium carbonate whiskers have a layered structure, each of which is made of magnesium, carbon, oxygen, with H2O in between each layer. When skeletons are superimposed within the same plane as a parallelepiped one, they grow into solid cuboid-shaped whiskers. When the parallelepiped skeletons planes combine with each other through the cascading links, they grow into hollow cylindrical whiskers.展开更多
The growth habit of the basic magnesium oxysulfate whisker was investigated based on the theoreticalmodelof anion coordination polyhedron growth units.It is found that typicalbasic magnesium oxysulfate whisker growth ...The growth habit of the basic magnesium oxysulfate whisker was investigated based on the theoreticalmodelof anion coordination polyhedron growth units.It is found that typicalbasic magnesium oxysulfate whisker growth is consistent with anion tetrahedralcoordination incorporation rules.The growth units of basic magnesium oxysulfate whiskers are [Mg-(OH)_4]^(2-) and HSO_4^-.[Mg-(OH)_4]^(2-) is the favorable growth unit and whisker growth is in the direction of the [Mg-(OH)_4]^(2-) combination.A plurality of [Mg-(OH)_4]^(2-) s combine and become a larger dimensionalgrowth unit in a one-dimensionaldirection.Then HSO_4^- and larger dimensionalgrowth units connect as basic magnesium sulfate whiskers,according to the structuralcharacteristics of the basic magnesium sulfate whisker,which can guide the synthesis of magnesium hydroxide whisker.展开更多
Crystals of semiconductor ZnO were fabricated by means of solid-vapor growth method-carbon thermal reduction. Powder X-ray diffraction and field emission scanning electron microscope were used to characterize the phas...Crystals of semiconductor ZnO were fabricated by means of solid-vapor growth method-carbon thermal reduction. Powder X-ray diffraction and field emission scanning electron microscope were used to characterize the phase and morphology of the samples. The results showed that the samples were wurtzite ZnO crystals and anisotropy of crystal growth relied on reaction temperature in solid-vapor process. The crystals synthesized at different temperatures were of short column-like shape, flat top hexagon pyramidal-like shape and polyhedron shape. The growth mechanisms of the above three kinds of crystal were consistent with the theory of growth basic structural unit of negative ion coordination polyhedron. At first, Zn2+ and four O2- form [Zn-O4]6- coordination tetrahedron at any temperature. Then, tetrahedrons stack in different ways into different morphology crystal at different temperatures.展开更多
With the expression theorem of convex polyhedron, this paper gives the general expression for the solutions in standard linear programming problems. And the calculation procedures in determining the optimal solutions ...With the expression theorem of convex polyhedron, this paper gives the general expression for the solutions in standard linear programming problems. And the calculation procedures in determining the optimal solutions are also given.展开更多
In this study,a systematic refinement method was developed for non-uniform Catmull-Clark subdivision surfaces to improve the quality of the surface at extraordinary points(EPs).The developed method modifies the eigenp...In this study,a systematic refinement method was developed for non-uniform Catmull-Clark subdivision surfaces to improve the quality of the surface at extraordinary points(EPs).The developed method modifies the eigenpolyhedron by designing the angles between two adjacent edges that contain an EP.Refinement rules are then formulated with the help of the modified eigenpolyhedron.Numerical experiments show that the method significantly improves the performance of the subdivision surface for non-uniform parameterization.展开更多
基金supported by the Natural Science Foundation of China under Grant No.61202154 and No.61133009the National Basic Research Project of China under Grant No.2011CB302203+2 种基金Shanghai Pujiang Program under Grant No.13PJ1404500the Science and Technology Commission of Shanghai Municipality Program under Grant No.13511505000the Open Project Program of the State Key Lab of CAD&CG of Zhejiang University under Grant No.A1401
文摘Regularized Boolean operations have been widely used in 3D modeling systems. However, evaluating Boolean operations may be quite numerically unstable and time consuming, especially for iterated set operations. A novel and unified technique is proposed in this paper for computing single and iterated set operations efficiently, robustly and exactly. An adaptive octree is combined with a nested constructive solid geometry (CSG) tree by this technique. The intersection handling is restricted to the cells in the octree where intersection actually occurs. Within those cells, a CSG tree template is instanced by the surfaces and the tree is converted to planebased binary space partitioning (BSP) for set evaluation; Moreover, the surface classification is restricted to the ceils in the octree where the surfaces only come from a model and are within the bounding-boxes of other polyhedrons. These two ways bring about the efficiency and scalability of the operations, in terms of runtime and memory. As all surfaces in such a cell have the same classification relation, they are classified as a whole. Robustness and exactness are achieved by integrating plane-based geometry representation with adaptive geometry predicate technique in intersection handling, and by applying divide-and-conquer arithmetic on surface classification. Experimental results demonstrate that the proposed approach can guarantee the robustness of Boolean computations and runs faster than other existing approaches.
基金This study was financially supported by the Program for the National Natural Science Foundation of China(Nos.NSFC-21901221,21671170,21673203 and U1904215)the Natural Science Foundation of Jiangsu Province(No.BK20190870)+1 种基金Changjiang Scholars Program of the Ministry of Education(No.Q2018270)the Top Talent Project of Yangzhou University.
文摘To improve the efficiency of oxygen electrolysis,exploiting bifunctional electrocatalysts with excellent activity and stability is extremely important due to the four-electron transfer dynamics of oxygen evolution reaction(OER)and oxygen reduction reaction(ORR).Herein,a series of yolk-shell hollow polyhedrons(YHPs)embedded with NiCoFe ternary alloy and metal oxides,which are named YHP-x(x=1,2,3,4),were reported.By controlled etching multi-layered zeolitic imidazolate frameworks and following pyrolytic integration,YHPs are endowed with mass transfer tunnels,accessible inner active sites,and good electrical conductivity.Due to the synergetic effect of the alloy,metal oxides and the yolk-shell structure,YHP-1 exhibits excellent ORR performance with a half-wave potential of 0.79 V and YHP-2 displays superior OER performance with a low overpotential of 257 mV at 10 mA cm−2.The strategy described in this work can be extended to a number of hollow/yolk-shell electrocatalysts for water splitting and metal–air batteries.
基金support from the Natural Science Foundation of Jilin Province(Grant No.20200201073JC)the National Natural Science Foundation of China(Grant No.52130101)+1 种基金Interdisciplinary Integration and Innovation Project of JLU(Grant No.JLUXKJC2021ZY01)the Fundamental Research Funds for the Central Universities.
文摘With the advantage of fast charge transfer,heterojunction engineering is identified as a viable method to reinforce the anodes'sodium storage performance.Also,vacancies can effectively strengthen the Na+adsorption ability and provide extra active sites for Na+adsorption.However,their synchronous engineering is rarely reported.Herein,a hybrid of Co_(0.85)Se/WSe_(2) heterostructure with Se vacancies and N-doped carbon polyhedron(CoWSe/NCP)has been fabricated for the first time via a hydrothermal and subsequent selenization strategy.Spherical aberration-corrected transmission electron microscopy confirms the phase interface of the Co_(0.85)Se/WSe_(2) heterostructure and the existence of Se vacancies.Density functional theory simulations reveal the accelerated charge transfer and enhanced Na+adsorption ability,which are contributed by the Co_(0.85)Se/WSe_(2) heterostructure and Se vacancies,respectively.As expected,the CoWSe/NCP anode in sodium-ion battery achieves outstanding rate capability(339.6 mAh g^(−1) at 20 A g^(−1)),outperforming almost all Co/W-based selenides.
基金supported by the National Natural Science Foundation of China(No.52073010)Beijing Natural Science Foundation(2214069)。
文摘Combining suitable microstructure and dielectric-magnetic synergy effect is conducive to achieve lightweight,broadband,and high-efficiency microwave absorbing materials within low filler loading.Herein,porous carbon polyhedrons coupled with bimetallic CoNi alloys were synthesized by using metalorganic frameworks(MOFs)as a template and subsequent pyrolysis treatment.Electromagnetic analysis indicated that the existence of metal Ni element could influence the wave attenuation capacity effectively,resulting in frequency selective wave absorption performance.Additionally,the pyrolysis temperature was also closely related to wave absorption intensity.The Co_(2)Ni_(1)/C/PVDF composites calcined at 800℃ possessed outstanding wave absorption performance at an ultra-low filler loading of 5 wt%.The minimum reflection loss value achieved-52 dB(10.8 GHz)under the matched thickness of 3 mm.Moreover,the broadest effective absorption bandwidth(RL<-10 dB)reached 6.2 dB(11.8-18 GHz)for Co/C-800/PVDF composites when the thickness turned into 2 mm.The remarkable wave attenuation ability was mainly ascribed to magnetic and dielectric loss,impedance matching as well as porous structure effect.
基金Supported from Southwest University, China (Grant No. SWNUB2005002)Key Laboratory of the Three Gorges Reservoir Region’s Eco-Environment within Ministry of Education, Chongqing University (Grant No. KLVF-2007-5)
文摘To gain insight into the structures and stability of F4F6 polyhedrons formed by squares and hexagons,a density functional theory study was performed on all isomers of F4F6 polyhedrons with sizes from 8 to 60.The calculated results demonstrate that the six squares tend to isolate from each other,i.e.these F4F6 polyhedrons obey the isolated square rule.Those isomers with fewer B44 bonds(square-square adjacencies) are more stable than those with more B44 bonds,i.e.they obey square adjacency penalty rule.Both of the two rules in F4F6 polyhedrons are in the same status as the isolated pentagon rule and pentagon adjacency penalty rule in F5F6 fullerenes and can be used to screen the lowest energy isomers of F4F6 polyhedrons as IPR and PAPR do in classic fullerenes.Structural analysis demonstrates that the pyramidalization of carbon atoms at the square-square adjacencies determines the stability of corresponding structures.
基金financially supported by the Natural Science Foundation of Henan Province of China(No.222300420252)Nanyang Normal University(Nos.2020ZX013 and 2020ZX014).
文摘Because of their large volume variation and inferior electrical conductivity,Mn_(3)O_(4)-based oxide anode materials have short cyclic lives and poor rate capability,which obstructs their development.In this study,we successfully prepared a Mn_(3)O_(4)/N-doped honeycomb carbon composite using a smart and facile synthetic method.The Mn_(3)O_(4)nanopolyhedra are grown on N-doped honeycomb carbon,which evidently mitigates the volume change in the charging and discharging processes but also improves the electrochemical reaction kinetics.More importantly,the Mn-O-C bond in the Mn_(3)O_(4)/N-doped honeycomb carbon composite benefits electrochemical reversibility.These features of the Mn_(3)O_(4)/N-doped honeycomb carbon(NHC)composite are responsible for its superior electrochemical performance.When used for Li-ion batteries,the Mn_(3)O_(4)/N-doped honeycomb carbon anode exhibits a high reversible capacity of 598 mAh·g^(−1)after 350 cycles at 1 A·g^(−1).Even at 2 A·g^(−1),the Mn_(3)O_(4)/NHC anode still delivers a high capacity of 472 mAh·g^(−1).This work provides a new prospect for synthesizing and developing manganese-based oxide materials for energy storage.
文摘It has been pointed out by the theoretic model of anion coordination polyhedra of growth units that the crystal form is dominated by the stability of combination of anion coordination polyhedra on the growth interface.The face has the fastest growth rate and disappears easily if the vertex of coordination polyhedron is pointed at.The face has the slowest growth rate and appears easily if the plane of coordination polyhedron is pointed at.The growth rate is in median for the face that the edge of coordination polyhedron is pointed at.A few of problems are discussed in the paper on the basis of this theory. (1)Several examples of the morphology of allomorph and homoeomorphism are given in the paper.There are three allomorphs of TiO 2 rutile,brookite and anatase.The morphology of these allomorphs are totally different because the stability of combination of octahedral [Ti O 6] 8- vary with the orientation and linked edges of coordination polyhedra.Another example is the homoeomorphism of cassiterite SnO 2.The orientation and combination of octahedral [Sn O 6] 8- in cassiterite are similar to that of octahedral [Ti O 6] 8- in rutile,so that cassiterite and rutile have similar morphology even for their form of twin and twin face.The combination of octahedral [Al O 6] 9- ,[Fe O 6] 9- and [Ti O 6] 8- respectively is similar at the orientation and linked form of coordination polyhedra in three crystals of corundum,hematite and ilmenite,so the same faces appear in these three crystals,resulted in similar morphology.
文摘After undergoing wireframe modeling, surface modeling and solid modeling, a unified product model, which holds a variety of constraints in engineering, supports design process, and unifies the wire frame, surface modeling, and solid modeling,is a general tendency of modeling technology. A discussion is presented here on how tobuild a unified product model by using the complex method. The concept of complex inalgebraic topology is introduced into the model and a new B-REP representation of thenon-manifold model is given --Identification Edge Structure. Based on it, some basicoperators and high-level operators are built. The model has a rigorous mathematicalbasis, and is flexible and easy to extend, and holds the lamina face, lamina edge andlamina vertex. As a result, the variety of constraints in engineering, such as parametricconstraints, optimization methods, fuzzy constraints, artificial intelligent, etc., can beadded to the system. The model may form the kernel for the implementation of the nextgeneration CAD system --intelligent CAD system.
基金supported by the National Nature Science Foundation of China (U1707603, 21625101, 21521005, U1507102)the National Key Research and Development Program of China (2017YFB0307303)+2 种基金the 973 program (Grant No. 2014CB932104)Beijing Natural Science Foundation (2182047)the Fundamental Research Funds for the Central Universities (ZY1709)
文摘It is of significance to design of stable and cost-effective electrocatalyst for water splitting with high efficiency in an alkaline medium.The major obstacles for practical application of water splitting devices are lack of high-efficiency and low-cost electrocatalysts with low overpotential for both HER and OER.In this paper,we report a NiFe alloy decorated NiCoO2 hollow polyhedron(denoted as Ni Fe–Ni Co O2)by using[NiFe(CN)6]- intercalated NiCo–LDH as precursor.As evidenced by the electrochemical active surface area,the resultant Ni Fe–Ni Co O2 composite shows unique hollow nanostructure,which can not only provide abundant mass transport channels,but also increase the contact area of the NiFe–Ni Co O2 material with the electrolyte.The overpotential(η)demand is 286 mV for OER and 102 mV for HER at the current density of 10 mA/cm2 in an alkaline medium of 1 M KOH for the NiFe/NiCoO2 composite.This work provides a new pathway for preparation of the highly efficient bifunctional electrocatalysts for water splitting.
文摘The architecture of the Great Pyramid at Giza is based on fascinating golden mean geometry. Recently the ratio of the in-sphere volume to the pyramid volume was calculated. One yields as result <em>R</em><sub><em>V</em></sub> = π <span style="white-space:nowrap;"><span style="white-space:nowrap;">⋅</span></span> <em><em style="white-space:normal;">φ</em></em><sup>5</sup>, where <img src="Edit_83decbce-7252-44ed-a822-fef13e43fd2a.bmp" alt="" /> is the golden mean. It is important that the number <em>φ</em><sup>5</sup> is a fundamental constant of nature describing phase transition from microscopic to cosmic scale. In this contribution the relatively small volume ratio of the Great Pyramid was compared to that of selected convex polyhedral solids such as the <em>Platonic </em>solids respectively the face-rich truncated icosahedron (bucky ball) as one of <em>Archimedes</em>’ solids leading to effective filling of the polyhedron by its in-sphere and therefore the highest volume ratio of the selected examples. The smallest ratio was found for the Great Pyramid. A regression analysis delivers the highly reliable volume ratio relation <img src="Edit_79e766ce-5580-4ae0-a706-570e0f3f1bd8.bmp" alt="" />, where <em>nF</em> represents the number of polyhedron faces and b approximates the silver mean. For less-symmetrical solids with a unique axis (tetragonal pyramids) the in-sphere can be replaced by a biaxial ellipsoid of maximum volume to adjust the <em>R</em><sub><em>V</em></sub> relation more reliably.
基金Supported by the National Natural Science Foundation and Mathematical "Tian Yuan" Foundation of China and the Natural Science Foundation of Fujian (Grant No. 10271097, TY10126033, F0110012)
文摘A new Koppelman-Leray-Norguet formula of (p,q) differential forms for a strictly pseudoconvex polyhedron with not necessarily smooth boundary on a Stein manifold is obtained, and an integral representation for the solution of -equation on this domain which does not involve integrals on boundary is given, so one can avoid complex estimates of boundary integrals.
基金the National Key Research and Devel-opment Program of China(Grant No.2018YFA0605902)the National Natural Science Foun-dation of China(Grant Nos.20212024,11872136)China Postdoctoral Science Foundation(Grant No.2020M670746).
文摘Freezing in ice rubble is a common phenomenon in cold regions,which can consolidate loose blocks and change their mechanical properties.To model the cohesive effect in frozen ice rubble,and to describe the fragmentation behavior with a large external forces exerted,a freeze-bond model based on the dilated polyhedral discrete element method(DEM)is proposed.Herein,imaginary bonding is initialized at the contact points to transmit forces and moments,and the initiation of the damage is detected using the hybrid fracture model.The model is validated through the qualitative agreement between the simulation results and the analytical solution of two bonding particles.To study the effect of freeze-bond on the floating ice rubble,punch-through tests were simulated on the ice rubble under freezing and nonfreezing conditions.The deformation and resistance of the ice rubble are investigated during indenter penetration.The influence of the internal friction coefficient on the strength of the ice rubble is determined.The results indicate that the proposed model can properly describe the consolidated ice rubble,and the freeze-bond effect is of great significance to the ice rubble properties.
基金supported by the National Basic Research Program of China("973" Program)(2012CB720000)the National Natural Science Foundation of China(11102020)the Program for New Century Excellent Talents in University and Beijing Higher Education Young Elite Teacher Project
文摘Shape modeling is fundamental to the analysis of dynamic environment and motion around asteroid. Chang'E- 2 successfully made a flyby of Asteroid 4179 Toutatis and obtained plenty of high-resolution images during the mis- sion. In this paper, the modeling method and preliminary model of Asteroid Toutatis are discussed. First, the optical images obtained by Chang'E-2 are analyzed. Terrain and silhouette features in images are described. Then, the modeling method based on previous radar model and preliminary information from optical images is proposed. A preliminary polyhedron model of Asteroid Toutatis is established. Finally, the spherical harmonic coefficients of Asteroid Toutatis based on the polyhedron model are obtained. Some parameters of model are analyzed and compared. Although the model proposed in this paper is only a preliminary model, this work offers a valuable reference for future high-resolution models.
基金Funded by the National Natural Science Foundation of China(No.51272207)
文摘From the perspective of growth units, the growth mechanism of Mg2(OH)2CO3.3H2O whisker is investigated in this paper. Results show that the growth morphology of Mg2(OH)2CO33H2O whisker is consistent with the model of anion coordination polyhedron growth units. The growth solution Raman shift of Mg2(OH)2CO;3H2O was monitored using Raman spectroscopy. The growth units are [Mg-(OH)4]2- and H2COv The growth process of Mg2(OH)2COf3H2O whisker is as follows: growth unit [Mg-(OH)4]2- first incorporates into the larger dimension [Mg-(OH)4]2-, then the [Mg-(OH)4]2-n combines with H2CO3 into a linear skeleton Mg2(OH)2CO3 in the same line. Mg2(OH)2CO3 combines with H2O by hydrogen bonds and ultimately transforms into Mg2(OH)2COf3H2O whisker. Magnesium carbonate whiskers have a layered structure, each of which is made of magnesium, carbon, oxygen, with H2O in between each layer. When skeletons are superimposed within the same plane as a parallelepiped one, they grow into solid cuboid-shaped whiskers. When the parallelepiped skeletons planes combine with each other through the cascading links, they grow into hollow cylindrical whiskers.
基金Funded by the National Natural Science Foundation of China(No.51272207)
文摘The growth habit of the basic magnesium oxysulfate whisker was investigated based on the theoreticalmodelof anion coordination polyhedron growth units.It is found that typicalbasic magnesium oxysulfate whisker growth is consistent with anion tetrahedralcoordination incorporation rules.The growth units of basic magnesium oxysulfate whiskers are [Mg-(OH)_4]^(2-) and HSO_4^-.[Mg-(OH)_4]^(2-) is the favorable growth unit and whisker growth is in the direction of the [Mg-(OH)_4]^(2-) combination.A plurality of [Mg-(OH)_4]^(2-) s combine and become a larger dimensionalgrowth unit in a one-dimensionaldirection.Then HSO_4^- and larger dimensionalgrowth units connect as basic magnesium sulfate whiskers,according to the structuralcharacteristics of the basic magnesium sulfate whisker,which can guide the synthesis of magnesium hydroxide whisker.
基金Funded by Shanxi Provincial Science Reasearch Foundation for Returned Scholars (No.2008-37)Shanxi Provincial Science Reasearch Foundation for Returned Scholars (No.2009-03)
文摘Crystals of semiconductor ZnO were fabricated by means of solid-vapor growth method-carbon thermal reduction. Powder X-ray diffraction and field emission scanning electron microscope were used to characterize the phase and morphology of the samples. The results showed that the samples were wurtzite ZnO crystals and anisotropy of crystal growth relied on reaction temperature in solid-vapor process. The crystals synthesized at different temperatures were of short column-like shape, flat top hexagon pyramidal-like shape and polyhedron shape. The growth mechanisms of the above three kinds of crystal were consistent with the theory of growth basic structural unit of negative ion coordination polyhedron. At first, Zn2+ and four O2- form [Zn-O4]6- coordination tetrahedron at any temperature. Then, tetrahedrons stack in different ways into different morphology crystal at different temperatures.
文摘With the expression theorem of convex polyhedron, this paper gives the general expression for the solutions in standard linear programming problems. And the calculation procedures in determining the optimal solutions are also given.
基金This work was supported by the National Key R&D Program of China,No.2020YFB1708900Natural Science Foundation of China,Nos.61872328 and 11801126.
文摘In this study,a systematic refinement method was developed for non-uniform Catmull-Clark subdivision surfaces to improve the quality of the surface at extraordinary points(EPs).The developed method modifies the eigenpolyhedron by designing the angles between two adjacent edges that contain an EP.Refinement rules are then formulated with the help of the modified eigenpolyhedron.Numerical experiments show that the method significantly improves the performance of the subdivision surface for non-uniform parameterization.