Visible-Light Communication(VLC) has the potential to provide dense and fast connectivity at low cost. In this paper we propose SFNet, a novel VLC-enabled hybrid data center network that extends the design of wireless...Visible-Light Communication(VLC) has the potential to provide dense and fast connectivity at low cost. In this paper we propose SFNet, a novel VLC-enabled hybrid data center network that extends the design of wireless Data Center Networks(DCNs) into three further dimensions:(1) fully wireless at the inter-rack level;(2) no need for a centralized control mechanism on wireless links;and(3) no need for any infrastructure-level alterations to data centers. Previous proposals typically cannot realize these three rationales simultaneously. To achieve this vision,the proposed SFNet augments fat-tree by organizing all racks into a wireless small-world network via VLC links. The use of VLC links eliminates hierarchical switches and cables in the wireless network, and thus reduces hardware investment and maintenance costs. To fully exploit the benefits of the topology of SFNet, we further propose its topology design and optimization method, routing scheme, and online flow scheduling algorithm. Comprehensive experiments indicate that SFNet exhibits good topological properties and network performance.展开更多
Understanding the mechanisms underlying cell-surface interaction is of fundamental importance for the rational design of scaffolds aiming at tissue engineering,tissue repair and neural regeneration applications.Here,w...Understanding the mechanisms underlying cell-surface interaction is of fundamental importance for the rational design of scaffolds aiming at tissue engineering,tissue repair and neural regeneration applications.Here,we examined patterns of neuroblastoma cells cultured in three-dimensional polymeric scaffolds obtained by two-photon lithography.Because of the intrinsic resolution of the technique,the micrometric cylinders composing the scaffold have a lateral step size of~200 nm,a surface roughness of around 20 nm,and large values of fractal dimension approaching 2.7.We found that cells in the scaffold assemble into separate groups with many elements per group.After cell wiring,we found that resulting networks exhibit high clustering,small path lengths,and small-world characteristics.These values of the topological characteristics of the network can potentially enhance the quality,quantity and density of information transported in the network compared to equivalent random graphs of the same size.This is one of the first direct observations of cells developing into 3D small-world networks in an artificial matrix.展开更多
A robust topology optimization design framework is developed to solve lightweight structural design problems under uncertain conditions. To enhance the calculation accuracy and flexibility of the statistical moments o...A robust topology optimization design framework is developed to solve lightweight structural design problems under uncertain conditions. To enhance the calculation accuracy and flexibility of the statistical moments of robust analysis, number theory integral method is applied to sample point selection and weight assignment. Both the structure topology optimization and number theory integral methods are combined to form a new robust topology optimization method. A suspension control arm problem is provided as a demonstration of robust topology optimization methods under loading uncertainties. Based on the results of deterministic and robust topology optimization, it is demonstrated that the proposed robust topology optimization method can produce a more robust design than that obtained by deterministic topology optimization. It is also found that this new approach is easy to apply in the existing commercial topology optimization software and thus feasible in practical engineering problems.展开更多
We present a study of the anti-centrifugal potential based on the incorporation of the quantum geometric potential of a surface [1] into the generalised anti-centrifugal potential [2]. As a basic variable we will use ...We present a study of the anti-centrifugal potential based on the incorporation of the quantum geometric potential of a surface [1] into the generalised anti-centrifugal potential [2]. As a basic variable we will use the unit normal to the surface. Then the total quantum effective potential appears to be the nonlinear sigma model plus positive terms. A 2d bilayer geometry smoothly connected by a neck is used to show that the anti-centrifugal potential creates topologically stable states.展开更多
In this paper,a parametric level-set-based topology optimization framework is proposed to concurrently optimize the structural topology at the macroscale and the effective infill properties at the micro/meso scale.The...In this paper,a parametric level-set-based topology optimization framework is proposed to concurrently optimize the structural topology at the macroscale and the effective infill properties at the micro/meso scale.The concurrent optimization is achieved by a computational framework combining a new parametric level set approach with mathematical programming.Within the proposed framework,both the structural boundary evolution and the effective infill property optimization can be driven by mathematical programming,which is more advantageous compared with the conventional partial differential equatiodriven level set approach.Moreover,the proposed approach will be more efficient in handling nonlinear problems with multiple constraints.Instead of using radial basis functions(RBF),in this paper,we propose to construct a new type of cardinal basis functions(CBF)for the level set function parameterization.The proposed CBF parameterization ensures an explicit impose of the lower and upper bounds of the design variables.This overcomes the intrinsic disadvantage of the conventional RBF-based parametric level set method,where the lower and upper bounds of the design variables oftentimes have to be set by trial and error;A variational distance regularization method is utilized in this research to regularize the level set function to be a desired distanceregularized shape.With the distance information embedded in the level set model,the wrapping boundary layer and the interior infill region can be naturally defined.The isotropic infill achieved via the mesoscale topology optimization is conformally fit into the wrapping boundary layer using the shape-preserving conformal mapping method,which leads to a hierarchical physical structure with optimized overall topology and effective infill properties.The proposed method is expected to provide a timely solution to the increasing demand for multiscale and multifunctional structure design.展开更多
The aim of this article is to present the contribution of Wu Wen-Tsün to Algebraic Topology and more precisely to the theory of characteristic classes. Several papers provide complete and welldocumented biography...The aim of this article is to present the contribution of Wu Wen-Tsün to Algebraic Topology and more precisely to the theory of characteristic classes. Several papers provide complete and welldocumented biography and academic career of Wu Wen-Tsün, in particular, Hudecek, 2014;O’Connor and Robertson, 2006;Wen-Tsün Wu’s Academic Career, 2006;Selected works of Wen-Tsun Wu, 2008.The author does not repeat the details provided in these papers concerning the Wu Wen-Tsün’s bibliography, we will just mention people involved in the Wu Wen-Tsün’s period in France.In addition to Wu Wen-Tsün’s papers, the Dieudonné’s book(Dieudonné, 1960) provides an excellent presentation of main results of Wu Wen-Tsün in Algebraic and Differential Topology. The author will use and abuse of this book(and refer to) when suitable.In the introduction, the author recalls mainly historical facts concerning the contribution of Wu Wen-Tsün to Algebraic Topology. The second section shows specifically the contribution of Wu WenTsün to the Stiefel-Whitney classes and introduces the third section, dealing with the(real) Wu classes.The author provides definition, properties as well as further developments and generalizations of the Wu classes. The fourth and fifth sections are devoted to recent applications: In Cobordism theory and in Mathematical Physics. The author notices that Wu classes have been used as well in other domains,in particular surgery theory(Madsen and Milgram, 1979). The last section concerns the complex Wu classes and shows that the more recent Mather classes coincide with the previously defined complex Wu classes, that is a result from Zhou(1994)(see also Liu, 1996).This article is devoted to the contribution of Wu Wen-Tsün to the theory of Characteristic Classes,which coincides with his "French period"(1947–1951). However, speaking of Algebraic Topology, it is worthwhile to mention the important contribution of Wu Wen-Tsün to the Theory of realization of complexes or manifolds in Euclidean spaces and of 展开更多
In recent years,the new technologies and discoveries on manufacturing materials have encouraged researchers to investigate the appearance of material properties that are not naturally available.Materials featuring a s...In recent years,the new technologies and discoveries on manufacturing materials have encouraged researchers to investigate the appearance of material properties that are not naturally available.Materials featuring a specific stiffness,or structures that combine non-structural and stmctural functions are applied in the aerospace,electronics and medical industry fields.Particularly,structures designed for dynamic actuation with reduced vibration response are the focus of this work.The bi-material and multifunctional concepts are considered for the design of a controlled piezoelectric actuator with vibration suppression by means of the topology optimization method(TOM).The bi-material piezoelectric actuator(BPEA)has its metallic host layer designed by the TOM,which defines the structural function,and the electric function is given by two piezo-ceramic layers that act as a sensor and an actuator coupled with a constant gain active velocity feedback control(AVFC).The AVFC,provided by the piezoelectric layers,affects the structural damping of the system through the velocity state variables readings in time domain.The dynamic equation analyzed throughout the optimization procedure is fully elaborated and implemented.The dynamic response for the rectangular fbur-noded finite element analysis is obtained by the Newmark's time-integration method,which is applied to the physical and the adjoint systems,given that the adjoint formulation is needed for the sensitivity analysis.A gradient-based optimization method is applied to minimize the displacement energy output measured at a predefined degree-of-freedom of the BPEA when a transient mechanical load is applied.Results are obtained for different control gain values to evaluate their influence on the final topology.展开更多
This paper presents a new robust topology optimization framework for hinge-free compliant mechanisms with spatially varying material uncertainties,which are described using a non-probabilistic bounded field model.Boun...This paper presents a new robust topology optimization framework for hinge-free compliant mechanisms with spatially varying material uncertainties,which are described using a non-probabilistic bounded field model.Bounded field uncertainties are efficiently represented by a reduced set of uncertain-but-bouncled coeflficients on the basis of the series expansion method.Robust topology optimization of compliant mechanisms is then defined to minimize the variation in output displacement under constraints of the mean displacement and predefined material volume.The nest optimization problem is solved using a gradient-based optimization algorithm.Numerical examples are presented to illustrate the effectiveness of the proposed method for circumventing hinges in topology optimization of compliant mechanisms.展开更多
This research focuses on the lightweight topology optimization method for structures under the premise of meeting the requirements of stability and vibration characteristics. A new topology optimization model with the...This research focuses on the lightweight topology optimization method for structures under the premise of meeting the requirements of stability and vibration characteristics. A new topology optimization model with the constraints of natural frequencies and critical buckling loads and the objective of minimizing the structural volume is established and solved based on the independent continuous mapping method. The eigenvalue equations and composite exponential filter functions are applied to convert the optimization formulation into a continuous, solvable mathematical programming model. In the process of topology optimization, suitable initial values of the filter functions are chosen to avoid local modes, and the dynamic frequency gap constraints are added in the optimal model to prevent mode switches. Furthermore, for the optimal structures with grey elements obtained by the continuous optimization model, the bisection-inverse iteration is applied to search the optimal discrete structures. Finally, a detailed scheme is given for the buckling and frequency topology optimization problem. Numerical examples illustrate that the modelling method of minimizing the economic index with given performance requirements is practical and feasible for multi-performance topology optimization problems.展开更多
This paper presents a manufacturing cost constrained topology optimization algorithm considering the laser powder bed additive manufacturing process.Topology optimization for additive manufacturing was recently extens...This paper presents a manufacturing cost constrained topology optimization algorithm considering the laser powder bed additive manufacturing process.Topology optimization for additive manufacturing was recently extensively studied,and many related topics have been addressed.However,metal additive manufacturing is an expensive process,and the high manufacturing cost severely hinders the widespread use of this technology.Therefore,the proposed algorithm in this research would provide an opportunity to balance the manufheturing cost while pursuing the superior structural perfonnance through topology optimization.Technically,the additive manufacturing cost model for laser powder bed-bascd process is established in this paper and real data is collected to support this model.Then,this cost model is transformed into a level set function-based expression,which is integrated into the level set topology optimization problem as a constraint.Therefore,by properly developing the sensitivity result,the metallic additive manufocturing part can be optimized with strictly constrained manufacturing cost.Effectiveness of the proposed algorithm is proved by numerical design examples.展开更多
Maximizing the fundamental eigenfrequency is an efficient means for vibrating structures to avoid resonance and noises.In this study,we develop an isogeometric analysis(IGA)-based level set model for the fonnulation a...Maximizing the fundamental eigenfrequency is an efficient means for vibrating structures to avoid resonance and noises.In this study,we develop an isogeometric analysis(IGA)-based level set model for the fonnulation and solution of topology optimization in cases with maximum eigenfrequency.The proposed method is based on a combination of level set method and IGA technique,which uses the non-uniform rational B-spline(NURBS),description of geometry,to perfonn analysis.The same NURBS is used for geometry representation,but also for IGA-based dynamic analysis and parameterization of the level set surface,that is,the level set function.The method is applied to topology optimization problems of maximizing the fundamental eigenfrequency for a given amount of material.A modal track method,that monitors a single target eigenmode is employed to prevent the exchange of eigenmode order number in eigenfrequency optimization.The validity and efficiency of the proposed method are illustrated by benchmark examples.展开更多
In this paper,we investigate the controllability problem of multi-agent systems with switching topology over finite fields.The multi-agent system is defined over finite fields,where agents process only values from a f...In this paper,we investigate the controllability problem of multi-agent systems with switching topology over finite fields.The multi-agent system is defined over finite fields,where agents process only values from a finite alphabet.Under leader-follower structure,one agent is selected as a leader for each subsystem.First,we prove that a multi-agent system with switching topology is controllable over a finite field if the graph of the subsystem is a spanning forest,and the size of the field is sufficiently large.Second,we show that,by appropriately selecting leaders,the multi-agent system with switching topology can be controllable over a finite field even if each of its subsystems is not controllable.Specifically,we show that the number of leaders for ensuring controllability of the switched multi-agent system is less than the minimum number of leaders for ensuring the controllability of all subsystems.Finally,it is proved that the multi-agent system is controllable over a finite field if the union of the graphs is a directed path graph or a star graph.展开更多
The firing of ceramic ware in chamber furnaces is a transient multiphysical process,including turbulence combustion and fluid flow in the gas space,convective and radiation heat transfer from the flue gases to the fur...The firing of ceramic ware in chamber furnaces is a transient multiphysical process,including turbulence combustion and fluid flow in the gas space,convective and radiation heat transfer from the flue gases to the furnace walls and ceramic ware,surface to surface radiation between the solid surfaces and conduction heat transfer in combination with endothermic or exothermic processes in the ceramic body.Models and conceptions for numerical analysis of that conjugate heat transfer(CHT)in such thermal aggregates are developed.They are validated on the base of information,obtained by in situ measurements at a furnace for firing of technical ceramic.Non-uniform thermal and fluid flow fields in the furnace space that cause problems in the surrounding walls and wastes at the ceramic ware are ascertained in it.An impossibility to improve the furnace operation at the existing construction and combustion installation is established.A variant for reconstruction of the furnace is investigated numerically.It includes changes of the number,power and topology of the burners and different arrangement of the ceramic ware in the furnace space.Uniform temperature fields and reduction of the specific fuel consumption at the suggested configuration of the thermal aggregate are established.展开更多
A new coordination polymer [Cu2(OH)(nbta)(tib)(H2 O)2]n(1, H3 nbta = 5-nitro-1,2,3-benzenetricarboxylic acid, tib = 1-(4 H-1,2,4-triazol-4-yl)-4-(imidazol-1-yl)benzene) constructed from dimeric Cu(Ⅱ) units has been s...A new coordination polymer [Cu2(OH)(nbta)(tib)(H2 O)2]n(1, H3 nbta = 5-nitro-1,2,3-benzenetricarboxylic acid, tib = 1-(4 H-1,2,4-triazol-4-yl)-4-(imidazol-1-yl)benzene) constructed from dimeric Cu(Ⅱ) units has been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction analysis. The compound crystallizes in monoclinic system, space group I2/c, with a = 17.8474(9), b = 11.7588(6), c = 21.9221(11) ?, β = 104.419(5)°, V = 4455.7(4) ?3 and Z = 8. Compound 1 is a three-dimensional structure constructed from dimeric Cu(Ⅱ) units and presents a 2-nodal(3,5)-connected net. Moreover, the thermal stability and solid UV-Vis absorption spectra have been investigated.展开更多
One new chiral zeolitic rAo-type metal-organic framework[Cd(L-ala)2]n(l)has been successfully synthesized based on L-alanine chiral ligand,which demonstrates the feasibility of fabricating MOF that integrates the 4-co...One new chiral zeolitic rAo-type metal-organic framework[Cd(L-ala)2]n(l)has been successfully synthesized based on L-alanine chiral ligand,which demonstrates the feasibility of fabricating MOF that integrates the 4-connected zeotype topology by the employment of Z-alanine.To the best of knowledge,it's the first report that metal-organic framework based on amino acid features the chiral zeolitic rho-type structure.Compound 1 was characterized by X-ray powder diffraction,elemental analysis and single-crystal X-ray diffraction.Crystal data:CbH9CdN2O4,Mr=285.55,cubic system,space group/432,a=24.0795(6),V=13961.9(10)A3,Z=48,Dc=1.630 Mg/m3,F(000)=6672,μ(MoKa)=1.865 mm-1,S=1.058,R=0.0271 and wR=0.0312 for 1870 observed reflections with I>2δ(I).The circular dichroism(CD)property of compound 1 was also investigated.展开更多
The low melt strength and poor crystallization behavior severely limit the processing and application of poly(lactic acid)(PLA)as biodegradable film materials.In this work,three-arm poly(L-lactic acid)(3A-PLLA)grafted...The low melt strength and poor crystallization behavior severely limit the processing and application of poly(lactic acid)(PLA)as biodegradable film materials.In this work,three-arm poly(L-lactic acid)(3A-PLLA)grafted silica nanoparticles with two kinds of topology structures were introduced into PLA matrix to improve the biodegradation performance.Different methods were used to characterize the structure of the grafted 3A-PLLA chains,the grafting density,and the thermal decomposition behavior of the nanoparticles.By varying the mass ratios of raw materials and altering the order of dropping solution in the reaction,high grafting densitytangled 3A-PLLA grafted SiO2 was synthesized as"3A-PLLA grafting to SiO2(GTS),while low grafting density-stretched 3A-PLLA grafted SiO2 was obtained as“SiO2 grafting to 3A-PLLA”(GTA).Topology of nanoparticles as well as the filler-matrix interaction is critically important to structure bio-nanocomposites with desirable properties.Thus,the GTS and GTA nanoparticles were introduced into PLA matrix to assess the effect.The SEM images showed the uniform dispersion of the modified nanoparticles,while the shear rheology results revealed that GTA nanoparticles made a more significant contribution on the melt-strengthening and relaxation time-extension of PLA.Moreover,it is suggested that GTA nanoparticles were more effective to act as a nucleating agent for PLA,which was proved by differential scanning calorimetry(DSC)and polarized optical microscopy(POM)researches.All of the improvements mentioned above of GTA nanocomposites can be ascribed to stronger entanglements between 3A-PLLA stretched by nano-SiO2 and PLA matrix.展开更多
An effective and simple design method for co-continuous composite material construction is proposed by using a hybrid methodology with triply periodic minimal surface (TPMS) cellular topology and the volumetric distan...An effective and simple design method for co-continuous composite material construction is proposed by using a hybrid methodology with triply periodic minimal surface (TPMS) cellular topology and the volumetric distance field (VDF). After generating a set of VDF-based features for the given exterior shape and desired internal core structure, a series of simple modifications in distance fields enabled us to obtain an arbitrarily-shaped complex co-continuous composite material computational model. Design results and manufactured prototypes through 3D printing technology show that the proposed methodology has the potential to open a new paradigm for producing multifunctional next generation co-continuous composite materials which are impossible to design and manufacture using traditional CAD and CAM.展开更多
文摘Visible-Light Communication(VLC) has the potential to provide dense and fast connectivity at low cost. In this paper we propose SFNet, a novel VLC-enabled hybrid data center network that extends the design of wireless Data Center Networks(DCNs) into three further dimensions:(1) fully wireless at the inter-rack level;(2) no need for a centralized control mechanism on wireless links;and(3) no need for any infrastructure-level alterations to data centers. Previous proposals typically cannot realize these three rationales simultaneously. To achieve this vision,the proposed SFNet augments fat-tree by organizing all racks into a wireless small-world network via VLC links. The use of VLC links eliminates hierarchical switches and cables in the wireless network, and thus reduces hardware investment and maintenance costs. To fully exploit the benefits of the topology of SFNet, we further propose its topology design and optimization method, routing scheme, and online flow scheduling algorithm. Comprehensive experiments indicate that SFNet exhibits good topological properties and network performance.
文摘Understanding the mechanisms underlying cell-surface interaction is of fundamental importance for the rational design of scaffolds aiming at tissue engineering,tissue repair and neural regeneration applications.Here,we examined patterns of neuroblastoma cells cultured in three-dimensional polymeric scaffolds obtained by two-photon lithography.Because of the intrinsic resolution of the technique,the micrometric cylinders composing the scaffold have a lateral step size of~200 nm,a surface roughness of around 20 nm,and large values of fractal dimension approaching 2.7.We found that cells in the scaffold assemble into separate groups with many elements per group.After cell wiring,we found that resulting networks exhibit high clustering,small path lengths,and small-world characteristics.These values of the topological characteristics of the network can potentially enhance the quality,quantity and density of information transported in the network compared to equivalent random graphs of the same size.This is one of the first direct observations of cells developing into 3D small-world networks in an artificial matrix.
基金Supported by the National Key Research and Development Program of China (2017YFB0103704)the National Natural Science Foundation of China (51675044).
文摘A robust topology optimization design framework is developed to solve lightweight structural design problems under uncertain conditions. To enhance the calculation accuracy and flexibility of the statistical moments of robust analysis, number theory integral method is applied to sample point selection and weight assignment. Both the structure topology optimization and number theory integral methods are combined to form a new robust topology optimization method. A suspension control arm problem is provided as a demonstration of robust topology optimization methods under loading uncertainties. Based on the results of deterministic and robust topology optimization, it is demonstrated that the proposed robust topology optimization method can produce a more robust design than that obtained by deterministic topology optimization. It is also found that this new approach is easy to apply in the existing commercial topology optimization software and thus feasible in practical engineering problems.
文摘We present a study of the anti-centrifugal potential based on the incorporation of the quantum geometric potential of a surface [1] into the generalised anti-centrifugal potential [2]. As a basic variable we will use the unit normal to the surface. Then the total quantum effective potential appears to be the nonlinear sigma model plus positive terms. A 2d bilayer geometry smoothly connected by a neck is used to show that the anti-centrifugal potential creates topologically stable states.
基金the National Science Foundation of the United States(Grant Nos.CMMI1462270 and CMMI1762287)Ford University Research Program(URP),and the start-up fund from the State University of New York at Stony Brook.
文摘In this paper,a parametric level-set-based topology optimization framework is proposed to concurrently optimize the structural topology at the macroscale and the effective infill properties at the micro/meso scale.The concurrent optimization is achieved by a computational framework combining a new parametric level set approach with mathematical programming.Within the proposed framework,both the structural boundary evolution and the effective infill property optimization can be driven by mathematical programming,which is more advantageous compared with the conventional partial differential equatiodriven level set approach.Moreover,the proposed approach will be more efficient in handling nonlinear problems with multiple constraints.Instead of using radial basis functions(RBF),in this paper,we propose to construct a new type of cardinal basis functions(CBF)for the level set function parameterization.The proposed CBF parameterization ensures an explicit impose of the lower and upper bounds of the design variables.This overcomes the intrinsic disadvantage of the conventional RBF-based parametric level set method,where the lower and upper bounds of the design variables oftentimes have to be set by trial and error;A variational distance regularization method is utilized in this research to regularize the level set function to be a desired distanceregularized shape.With the distance information embedded in the level set model,the wrapping boundary layer and the interior infill region can be naturally defined.The isotropic infill achieved via the mesoscale topology optimization is conformally fit into the wrapping boundary layer using the shape-preserving conformal mapping method,which leads to a hierarchical physical structure with optimized overall topology and effective infill properties.The proposed method is expected to provide a timely solution to the increasing demand for multiscale and multifunctional structure design.
文摘The aim of this article is to present the contribution of Wu Wen-Tsün to Algebraic Topology and more precisely to the theory of characteristic classes. Several papers provide complete and welldocumented biography and academic career of Wu Wen-Tsün, in particular, Hudecek, 2014;O’Connor and Robertson, 2006;Wen-Tsün Wu’s Academic Career, 2006;Selected works of Wen-Tsun Wu, 2008.The author does not repeat the details provided in these papers concerning the Wu Wen-Tsün’s bibliography, we will just mention people involved in the Wu Wen-Tsün’s period in France.In addition to Wu Wen-Tsün’s papers, the Dieudonné’s book(Dieudonné, 1960) provides an excellent presentation of main results of Wu Wen-Tsün in Algebraic and Differential Topology. The author will use and abuse of this book(and refer to) when suitable.In the introduction, the author recalls mainly historical facts concerning the contribution of Wu Wen-Tsün to Algebraic Topology. The second section shows specifically the contribution of Wu WenTsün to the Stiefel-Whitney classes and introduces the third section, dealing with the(real) Wu classes.The author provides definition, properties as well as further developments and generalizations of the Wu classes. The fourth and fifth sections are devoted to recent applications: In Cobordism theory and in Mathematical Physics. The author notices that Wu classes have been used as well in other domains,in particular surgery theory(Madsen and Milgram, 1979). The last section concerns the complex Wu classes and shows that the more recent Mather classes coincide with the previously defined complex Wu classes, that is a result from Zhou(1994)(see also Liu, 1996).This article is devoted to the contribution of Wu Wen-Tsün to the theory of Characteristic Classes,which coincides with his "French period"(1947–1951). However, speaking of Algebraic Topology, it is worthwhile to mention the important contribution of Wu Wen-Tsün to the Theory of realization of complexes or manifolds in Euclidean spaces and of
基金CNPq(National Council for Scientific and Technological Development)under grant 302658/2018-1 and CAPES project number A023-2013.
文摘In recent years,the new technologies and discoveries on manufacturing materials have encouraged researchers to investigate the appearance of material properties that are not naturally available.Materials featuring a specific stiffness,or structures that combine non-structural and stmctural functions are applied in the aerospace,electronics and medical industry fields.Particularly,structures designed for dynamic actuation with reduced vibration response are the focus of this work.The bi-material and multifunctional concepts are considered for the design of a controlled piezoelectric actuator with vibration suppression by means of the topology optimization method(TOM).The bi-material piezoelectric actuator(BPEA)has its metallic host layer designed by the TOM,which defines the structural function,and the electric function is given by two piezo-ceramic layers that act as a sensor and an actuator coupled with a constant gain active velocity feedback control(AVFC).The AVFC,provided by the piezoelectric layers,affects the structural damping of the system through the velocity state variables readings in time domain.The dynamic equation analyzed throughout the optimization procedure is fully elaborated and implemented.The dynamic response for the rectangular fbur-noded finite element analysis is obtained by the Newmark's time-integration method,which is applied to the physical and the adjoint systems,given that the adjoint formulation is needed for the sensitivity analysis.A gradient-based optimization method is applied to minimize the displacement energy output measured at a predefined degree-of-freedom of the BPEA when a transient mechanical load is applied.Results are obtained for different control gain values to evaluate their influence on the final topology.
基金the National Key R&D Program of China(Grant No.2017YFB0203604)the National Natural Science Foundation of China(Grant No.11472215).
文摘This paper presents a new robust topology optimization framework for hinge-free compliant mechanisms with spatially varying material uncertainties,which are described using a non-probabilistic bounded field model.Bounded field uncertainties are efficiently represented by a reduced set of uncertain-but-bouncled coeflficients on the basis of the series expansion method.Robust topology optimization of compliant mechanisms is then defined to minimize the variation in output displacement under constraints of the mean displacement and predefined material volume.The nest optimization problem is solved using a gradient-based optimization algorithm.Numerical examples are presented to illustrate the effectiveness of the proposed method for circumventing hinges in topology optimization of compliant mechanisms.
基金the National Natural Science Foundation of China (11872080, 11172013)Natural Science Foundation of Beijing Municipality (3192005)Beijing Education Committee Development Project (SQKM201610005001).
文摘This research focuses on the lightweight topology optimization method for structures under the premise of meeting the requirements of stability and vibration characteristics. A new topology optimization model with the constraints of natural frequencies and critical buckling loads and the objective of minimizing the structural volume is established and solved based on the independent continuous mapping method. The eigenvalue equations and composite exponential filter functions are applied to convert the optimization formulation into a continuous, solvable mathematical programming model. In the process of topology optimization, suitable initial values of the filter functions are chosen to avoid local modes, and the dynamic frequency gap constraints are added in the optimal model to prevent mode switches. Furthermore, for the optimal structures with grey elements obtained by the continuous optimization model, the bisection-inverse iteration is applied to search the optimal discrete structures. Finally, a detailed scheme is given for the buckling and frequency topology optimization problem. Numerical examples illustrate that the modelling method of minimizing the economic index with given performance requirements is practical and feasible for multi-performance topology optimization problems.
文摘This paper presents a manufacturing cost constrained topology optimization algorithm considering the laser powder bed additive manufacturing process.Topology optimization for additive manufacturing was recently extensively studied,and many related topics have been addressed.However,metal additive manufacturing is an expensive process,and the high manufacturing cost severely hinders the widespread use of this technology.Therefore,the proposed algorithm in this research would provide an opportunity to balance the manufheturing cost while pursuing the superior structural perfonnance through topology optimization.Technically,the additive manufacturing cost model for laser powder bed-bascd process is established in this paper and real data is collected to support this model.Then,this cost model is transformed into a level set function-based expression,which is integrated into the level set topology optimization problem as a constraint.Therefore,by properly developing the sensitivity result,the metallic additive manufocturing part can be optimized with strictly constrained manufacturing cost.Effectiveness of the proposed algorithm is proved by numerical design examples.
基金the National Natural Science Foundation of China(Grant No.51675197).
文摘Maximizing the fundamental eigenfrequency is an efficient means for vibrating structures to avoid resonance and noises.In this study,we develop an isogeometric analysis(IGA)-based level set model for the fonnulation and solution of topology optimization in cases with maximum eigenfrequency.The proposed method is based on a combination of level set method and IGA technique,which uses the non-uniform rational B-spline(NURBS),description of geometry,to perfonn analysis.The same NURBS is used for geometry representation,but also for IGA-based dynamic analysis and parameterization of the level set surface,that is,the level set function.The method is applied to topology optimization problems of maximizing the fundamental eigenfrequency for a given amount of material.A modal track method,that monitors a single target eigenmode is employed to prevent the exchange of eigenmode order number in eigenfrequency optimization.The validity and efficiency of the proposed method are illustrated by benchmark examples.
基金National Natural Science Foundation of China(Grant Nos.61375120,61533001,61374199).
文摘In this paper,we investigate the controllability problem of multi-agent systems with switching topology over finite fields.The multi-agent system is defined over finite fields,where agents process only values from a finite alphabet.Under leader-follower structure,one agent is selected as a leader for each subsystem.First,we prove that a multi-agent system with switching topology is controllable over a finite field if the graph of the subsystem is a spanning forest,and the size of the field is sufficiently large.Second,we show that,by appropriately selecting leaders,the multi-agent system with switching topology can be controllable over a finite field even if each of its subsystems is not controllable.Specifically,we show that the number of leaders for ensuring controllability of the switched multi-agent system is less than the minimum number of leaders for ensuring the controllability of all subsystems.Finally,it is proved that the multi-agent system is controllable over a finite field if the union of the graphs is a directed path graph or a star graph.
基金the Operational Programme“Science and education for smart growth”2014-2020 of the European Union cofounded by the European Social Fund through the project BG05M2ОP001-2.009-0015“Support for the development of capacity of doctoral students and young researchers in the field of engineering,natural and mathematical sciences”.
文摘The firing of ceramic ware in chamber furnaces is a transient multiphysical process,including turbulence combustion and fluid flow in the gas space,convective and radiation heat transfer from the flue gases to the furnace walls and ceramic ware,surface to surface radiation between the solid surfaces and conduction heat transfer in combination with endothermic or exothermic processes in the ceramic body.Models and conceptions for numerical analysis of that conjugate heat transfer(CHT)in such thermal aggregates are developed.They are validated on the base of information,obtained by in situ measurements at a furnace for firing of technical ceramic.Non-uniform thermal and fluid flow fields in the furnace space that cause problems in the surrounding walls and wastes at the ceramic ware are ascertained in it.An impossibility to improve the furnace operation at the existing construction and combustion installation is established.A variant for reconstruction of the furnace is investigated numerically.It includes changes of the number,power and topology of the burners and different arrangement of the ceramic ware in the furnace space.Uniform temperature fields and reduction of the specific fuel consumption at the suggested configuration of the thermal aggregate are established.
基金supported by the National Natural Science Foundation of China(21401097).
文摘A new coordination polymer [Cu2(OH)(nbta)(tib)(H2 O)2]n(1, H3 nbta = 5-nitro-1,2,3-benzenetricarboxylic acid, tib = 1-(4 H-1,2,4-triazol-4-yl)-4-(imidazol-1-yl)benzene) constructed from dimeric Cu(Ⅱ) units has been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction analysis. The compound crystallizes in monoclinic system, space group I2/c, with a = 17.8474(9), b = 11.7588(6), c = 21.9221(11) ?, β = 104.419(5)°, V = 4455.7(4) ?3 and Z = 8. Compound 1 is a three-dimensional structure constructed from dimeric Cu(Ⅱ) units and presents a 2-nodal(3,5)-connected net. Moreover, the thermal stability and solid UV-Vis absorption spectra have been investigated.
基金National Natural Science Foundation of China(No.21601080).
文摘One new chiral zeolitic rAo-type metal-organic framework[Cd(L-ala)2]n(l)has been successfully synthesized based on L-alanine chiral ligand,which demonstrates the feasibility of fabricating MOF that integrates the 4-connected zeotype topology by the employment of Z-alanine.To the best of knowledge,it's the first report that metal-organic framework based on amino acid features the chiral zeolitic rho-type structure.Compound 1 was characterized by X-ray powder diffraction,elemental analysis and single-crystal X-ray diffraction.Crystal data:CbH9CdN2O4,Mr=285.55,cubic system,space group/432,a=24.0795(6),V=13961.9(10)A3,Z=48,Dc=1.630 Mg/m3,F(000)=6672,μ(MoKa)=1.865 mm-1,S=1.058,R=0.0271 and wR=0.0312 for 1870 observed reflections with I>2δ(I).The circular dichroism(CD)property of compound 1 was also investigated.
基金the National Natural Science Foundation of China(Nos.51721091,21674069,and 21174092).
文摘The low melt strength and poor crystallization behavior severely limit the processing and application of poly(lactic acid)(PLA)as biodegradable film materials.In this work,three-arm poly(L-lactic acid)(3A-PLLA)grafted silica nanoparticles with two kinds of topology structures were introduced into PLA matrix to improve the biodegradation performance.Different methods were used to characterize the structure of the grafted 3A-PLLA chains,the grafting density,and the thermal decomposition behavior of the nanoparticles.By varying the mass ratios of raw materials and altering the order of dropping solution in the reaction,high grafting densitytangled 3A-PLLA grafted SiO2 was synthesized as"3A-PLLA grafting to SiO2(GTS),while low grafting density-stretched 3A-PLLA grafted SiO2 was obtained as“SiO2 grafting to 3A-PLLA”(GTA).Topology of nanoparticles as well as the filler-matrix interaction is critically important to structure bio-nanocomposites with desirable properties.Thus,the GTS and GTA nanoparticles were introduced into PLA matrix to assess the effect.The SEM images showed the uniform dispersion of the modified nanoparticles,while the shear rheology results revealed that GTA nanoparticles made a more significant contribution on the melt-strengthening and relaxation time-extension of PLA.Moreover,it is suggested that GTA nanoparticles were more effective to act as a nucleating agent for PLA,which was proved by differential scanning calorimetry(DSC)and polarized optical microscopy(POM)researches.All of the improvements mentioned above of GTA nanocomposites can be ascribed to stronger entanglements between 3A-PLLA stretched by nano-SiO2 and PLA matrix.
基金Scientific Research Foundation of the Higher Education Institutions of Hainan Province of China (Grant No. Hnky2018-101).
文摘An effective and simple design method for co-continuous composite material construction is proposed by using a hybrid methodology with triply periodic minimal surface (TPMS) cellular topology and the volumetric distance field (VDF). After generating a set of VDF-based features for the given exterior shape and desired internal core structure, a series of simple modifications in distance fields enabled us to obtain an arbitrarily-shaped complex co-continuous composite material computational model. Design results and manufactured prototypes through 3D printing technology show that the proposed methodology has the potential to open a new paradigm for producing multifunctional next generation co-continuous composite materials which are impossible to design and manufacture using traditional CAD and CAM.