In this paper, we discuss the optimal insurance in the presence of background risk while the insured is ambiguity averse and there exists belief heterogeneity between the insured and the insurer. We give the optimal i...In this paper, we discuss the optimal insurance in the presence of background risk while the insured is ambiguity averse and there exists belief heterogeneity between the insured and the insurer. We give the optimal insurance contract when maxing the insured’s expected utility of his/her remaining wealth under the smooth ambiguity model and the heterogeneous belief form satisfying the MHR condition. We calculate the insurance premium by using generalized Wang’s premium and also introduce a series of stochastic orders proposed by [1] to describe the relationships among the insurable risk, background risk and ambiguity parameter. We obtain the deductible insurance is the optimal insurance while they meet specific dependence structures.展开更多
Ultrastable metallic glasses(SMGs)exhibit enhanced stability comparable to those of conventional glasses aged for thousands of years.The ability to understand why certain alloy compositions and processing conditions g...Ultrastable metallic glasses(SMGs)exhibit enhanced stability comparable to those of conventional glasses aged for thousands of years.The ability to understand why certain alloy compositions and processing conditions generate an SMG is an emerging challenge.Herein,amplitude-modulation dynamic atomic force microscopy was utilized for tracking the structure of Zr_(50)Cu_(50),Zr_(50)Cu_(44.5)Al_(5.5)and Zr_(50)Cu_(41.5)Al_(5.5)Mo_(3) thin film metallic glasses(TFMGs)that were produced by direct current magnetron sputtering at room temperature with the rate of deposition being the only variable.The transition in stability from bulkto SMG-like behavior resides in the change of relaxation mechanism as the deposition rate is decreased.The formation of SMGs is directly linked with the degree of structural heterogeneity,whereby MGs with greater heterogeneity have a higher potential to form SMGs with more significant enhancement in stability.Slower deposition rates,however,are required to yield the more homogenous structure and lower energy state underlying the ultrastability.Ultrastability is closely linked with the geometric shape and distribution of loosely packed phases,whereby SMGs containing more slender loosely packed phases with a more skewed distribution achieve more significant improvements in stability.This work not only provides direct evidence of the structure of SMGs,but also opens new horizons for the design of SMGs.展开更多
Understanding mechanical relaxation, such as primary(α) and secondary(β) relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses....Understanding mechanical relaxation, such as primary(α) and secondary(β) relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses. At a fundamental level, relaxation, plastic deformation, glass transition, and crystallization of metallic glasses are intimately linked to each other, which can be related to atomic packing, inter-atomic diffusion, and cooperative atom movement. Conceptually, βrelaxation is usually associated with structural heterogeneities intrinsic to metallic glasses. However, the details of such structural heterogeneities, being masked by the meta-stable disordered long-range structure, are yet to be understood. In this paper, we briefly review the recent experimental and simulation results that were attempted to elucidate structural heterogeneities in metallic glasses within the framework of β relaxation. In particular, we will discuss the correlation amongβ relaxation, structural heterogeneity, and mechanical properties of metallic glasses.展开更多
Due to the complex diagenesis process,basalt usually contains defects in the form of amygdales formed by diagenetic bubbles,which affect its mechanical properties.In this study,a synthetic rock mass method(SRM)based o...Due to the complex diagenesis process,basalt usually contains defects in the form of amygdales formed by diagenetic bubbles,which affect its mechanical properties.In this study,a synthetic rock mass method(SRM)based on the combination of discrete fracture network(DFN)and finite-discrete element method(FDEM)is applied to characterizing the amygdaloidal basalt,and to systematically exploring the effects of the development characteristics of amygdales and sample sizes on the mechanical properties of basalt.The results show that with increasing amygdale content,the elastic modulus(E)increases linearly,while the uniaxial compressive strength(UCS)shows an exponential or logarithmic decay.When the orientation of amygdales is between 0°and 90°,basalt shows a relatively pronounced strength and stiffness anisotropy.Based on the analysis of the geometric and mechanical properties,the representative element volume(REV)size of amygdaloidal basalt blocks is determined to be 200 mm,and the mechanical properties obtained on this scale can be regarded as the properties of the equivalent continuum.The results of this research are of value to the understanding of the mechanical properties of amygdaloidal basalt,so as to guide the formulation of engineering design schemes more accurately.展开更多
We report a process route to fabricate an Al–Al interpenetrating-phase composite by combining the Al–Mg–Mn–Sc–Zr lattice structure and Al_(84)Ni_(7)Gd_(6)Co_(3)nanostructured structure. The lattice structure was ...We report a process route to fabricate an Al–Al interpenetrating-phase composite by combining the Al–Mg–Mn–Sc–Zr lattice structure and Al_(84)Ni_(7)Gd_(6)Co_(3)nanostructured structure. The lattice structure was produced by the selective laser melting and subsequently filled with the Al_(84)Ni_(7)Gd_(6)Co_(3)amorphous powder, and finally the mixture was used for hot extrusion to produce bulk samples. The results show that the composites achieve a high densification and good interface bonding due to the element diffusion and plastic deformation during hot extrusion.The bulk samples show a heterogeneous structure with a combination of honeycomb lattice structure with an average grain size of less than1 μm and nanostructured area with a high volume fraction of nanometric intermetallics and nanograin α-Al. The heterogeneous structure leads to a bimodal mechanical zone with hard area and soft area giving rise to high strength and acceptable plasticity, where the compressive yield strength and the compressive plasticity can reach ~745 MPa and ~30%, respectively. The high strength can be explained by the rule of mixture,the grain boundary strengthening, and the back stress, while the acceptable plasticity is mainly owing to the confinement effect of the nanostructured area retarding the brittle fracture behavior.展开更多
In order to mimic the natural heterogeneity of native tissue and provide a better microenvironment for cell culturing,multi-material bioprinting has become a common solution to construct tissue models in vitro.With th...In order to mimic the natural heterogeneity of native tissue and provide a better microenvironment for cell culturing,multi-material bioprinting has become a common solution to construct tissue models in vitro.With the embedded printing method,complex 3D structure can be printed using soft biomaterials with reasonable shape fidelity.However,the current sequential multi-material embedded printing method faces a major challenge,which is the inevitable trade-off between the printed structural integrity and printing precision.Here,we propose a simultaneous multi-material embedded printing method.With this method,we can easily print firmly attached and high-precision multilayer structures.With multiple individually controlled nozzles,different biomaterials can be precisely deposited into a single crevasse,minimizing uncontrolled squeezing and guarantees no contamination of embedding medium within the structure.We analyse the dynamics of the extruded bioink in the embedding medium both analytically and experimentally,and quantitatively evaluate the effects of printing parameters including printing speed and rheology of embedding medium,on the 3D morphology of the printed filament.We demonstrate the printing of double-layer thin-walled structures,each layer less than 200μm,as well as intestine and liver models with 5%gelatin methacryloyl that are crosslinked and extracted from the embedding medium without significant impairment or delamination.The peeling test further proves that the proposed method offers better structural integrity than conventional sequential printing methods.The proposed simultaneous multi-material embedded printing method can serve as a powerful tool to support the complex heterogeneous structure fabrication and open unique prospects for personalized medicine.展开更多
Transport properties and the associated structural heterogeneity of room temperature aqueous ionic liquids and especially of super-concentrated electrolyte aqueous solutions have received increasing attention,due to t...Transport properties and the associated structural heterogeneity of room temperature aqueous ionic liquids and especially of super-concentrated electrolyte aqueous solutions have received increasing attention,due to their potential application in ionic battery.This paper briefly reviews the results reported mainly since 2010 about the liquid-liquid separation,aggregation of polar and apolar domains in neat RTILs,and solvent clusters and 3D networks chiefly constructed by anions in super-concentrated electrolyte solutions.At the same time,the dominating effect of desolvation process of metal ions at electrode/electrolyte interface upon the transport of metal ions is stressed.This paper also presents the current understanding of how water affects the anion-cation interaction,structural heterogeneities,the structure of primary coordination sheath of metal ions and consequently their transport properties in free water-poor electrolytes.展开更多
Metallic glasses are spatially heterogeneous at the nanometer scale.However,the effects of external excitation on their structural and mechanical heterogeneity and the correlation to their properties are still unresol...Metallic glasses are spatially heterogeneous at the nanometer scale.However,the effects of external excitation on their structural and mechanical heterogeneity and the correlation to their properties are still unresolved.Nanoindentation,atomic force microscopy(AFM) and high-resolution transmis sion elec tron micro scopy(HRTEM) were carried out to explore the effects of cryogenic thermal cycling(CTC) on mechanical/structural heterogeneity,nano sc ale creep deformation and optical properties of nano structured metallic glass thin films(MGTFs).The results indicate that CTC treatment alters the distribution fluctuations of hardness/modulus and energy dissipation and results in an increase-then-decrease variation in mechanical heterogeneity.By applying Maxwell-Voigt model,it can be shown that CTC treatment results in a remarkable activation of more defects with longer relaxation time in soft regions but has only a slight effect on defects in hard regions.In addition,CTC treatment increases the transition time from primary-state stage to steady-state stage during creep deformation.The enhanced optical reflectivity of the MGTFs after 15 thermal cycles can be attributed to increased aggregation of Cu and Ni elements.The results of this study shed new light on understanding mechanical/structural heterogeneity and its influence on nanoscale creep deformation and optical characteristics of nanostructured MGTFs,and facilitate the design of high-performance nanostructured MGTFs.展开更多
Heterogeneous nuclear ribonucleoprotein (hnRNP) C plays a key role in RNA processing but also exerts a dominant negative effect on responses to 1,25-dihydroxyvitamin D (1,25(OH)2D) by functioning as a vitamin D ...Heterogeneous nuclear ribonucleoprotein (hnRNP) C plays a key role in RNA processing but also exerts a dominant negative effect on responses to 1,25-dihydroxyvitamin D (1,25(OH)2D) by functioning as a vitamin D response element-binding protein (VDRE-BP). hnRNPC acts a tetramer of hnRNPC1 (huC1) and hnRNPC2 (huC2), and organization of these subunits is critical to in vivo nucleic acid-binding. Overexpression of either huC1 or huC2 in human osteoblasts is sufficient to confer VDRE-BP suppression of 1,25(OH)2D-mediated transcription. However, huC1 or huC2 alone did not suppress 1,25(OH)2D-induced transcription in mouse osteoblastic cells. By contrast, overexpression of huC1 and huC2 in combination or transfection with a bone-specific polycistronic vector using a "self-cleaving" 2A peptide to co-express huC1/C2 suppressed 1,25D-mediated induction of osteoblast target gene expression. Structural diversity of hnRNPC between human/NWPs and mouse/rat/rabbit/dog was investigated by analysis of sequence variations within the hnRNP CLZ domain. The predicted loss of distal helical function in hnRNPC from lower species provides an explanation for the altered interaction between huC1/C2 and their mouse counterparts. These data provide new evidence of a role for hnRNPC1/C2 in 1,25(OH)2D-driven gene expression, and further suggest that species-specific tetramerization is a crucial determinant of its actions as a regulator of VDR-directed transactivation.展开更多
The retarded kinetics of oxygen evolution on electrodes is a bottleneck for electrochemical energy conversion and storage systems.NiFe-based electrocatalysts provide a cost-effective choice to confront this challenge....The retarded kinetics of oxygen evolution on electrodes is a bottleneck for electrochemical energy conversion and storage systems.NiFe-based electrocatalysts provide a cost-effective choice to confront this challenge.However,there is a lack of facile techniques for depositing compact catalytic films of high coverage and possessing a state-of-the-art performance,which is especially desired in photoelectrochemical(PEC)systems.Herein,we demonstrate a spray pyrolysis(SP)route to address this issue,featuring the kinetic selective preparation towards the desired catalytic-active material.Differing from reported SP protocols which only produce inactive oxides,this approach directly generates a unique composite film consisting of NiFe layered oxyhydroxides and amorphous oxides,exhibiting an overpotential as small as 255 mV(10 mA cm^(−2))and a turnover frequency of∼0.4 s^(−1)per metal atom.By using such a facile protocol,the surface rate-limiting issue of BiVO_(4)photoanodes can be effectively resolved,resulting in a charge injection efficiency of over 90%.Considering this deposition directly start from simple nitrates but only takes several seconds to complete,we believe it can be developed as a widely applicable and welcomed functionalization technique for diverse electrochemical devices.展开更多
The heterogeneous magnesium(Mg) matrix nanocomposite with dispersed soft phase exhibits high strength and toughness. Herein, the deformation behavior and failure process were investigated to reveal the unique mechanic...The heterogeneous magnesium(Mg) matrix nanocomposite with dispersed soft phase exhibits high strength and toughness. Herein, the deformation behavior and failure process were investigated to reveal the unique mechanical behavior of the heterogeneous microstructure under compression. The extensive plastic deformation is accompanied by the flattening and tilting of the soft phase, inhibiting strain localization and leading to strain hardening. Moreover, a stable crack multiplication process is activated, which endows high damage tolerance to the heterogeneous Mg matrix nanocomposites. The final failure of the composite is caused by crack coalescence in the shear plane along a tortuous path. The presence of dispersed soft phases within the hard matrix induces a noticeable change in mechanical response. Especially,the malleability of the heterogeneous Mg matrix nanocomposite is two and ten times higher than that of pure Mg and the homogeneous Mg matrix nanocomposite, respectively. The current study provides a novel strategy to break the trade-off between strength and toughness in metal matrix nanocomposites.展开更多
With the rapid growth of network technology, the methods and types of cyber-attacks are increasing rapidly. Traditional static passive defense technologies focus on external security and known threats to the target sy...With the rapid growth of network technology, the methods and types of cyber-attacks are increasing rapidly. Traditional static passive defense technologies focus on external security and known threats to the target system and cannot resist advanced persistent threats. To solve the situation that cyberspace security is easy to attack and difficult to defend, Chinese experts on cyberspace security proposed an innovative theory called mimic defense, it is an active defense technology that employs “Dynamic, Heterogeneous, Redundant” architecture to defense attacks. This article first briefly describes the classic network defense technology and Moving Target Defense (MTD). Next, it mainly explains in detail the principles of the mimic defense based on the DHR architecture and analyzes the attack surface of DHR architecture. This article also includes applications of mimic defense technology, such as mimic routers, and mimic web defense systems. Finally, it briefly summarizes the existing research on mimic defense, expounds the problems that need to be solved in mimic defense, and looks forward to the future development of mimic defense.展开更多
Despite the great efforts dedicated to metallic glasses (MGs), their structure still remains a mystery to be understood. With comparison to the existing mJciomechanical models, such as the free-volume and shear tran...Despite the great efforts dedicated to metallic glasses (MGs), their structure still remains a mystery to be understood. With comparison to the existing mJciomechanical models, such as the free-volume and shear transformation zone (STZ) models, we first discuss in this article our recently proposed 'core-shell' model, which contains a solid-like matrix and liquid-like inclusions. This serves as the theoretical basis to understand the structural heterogeneity in MGs in our analytical framework. After that, a scanning ultrafast nanoindentation technique is used to map out the structure heterogeneity in a Zr-based bulk metallic glass (BMG). With these ongoing research efforts, we hope that more research work could be stimulated in the pursuit of the structure-property relation in MGs.展开更多
Mechanical cycling is one of the effective methods to rejuvenate metallic glasses(MGs)and improve their mechanical properties.The anelastic origin of the rejuvenation by mechanical cycling in a La_(30)Ce_(30)Ni_(10)Al...Mechanical cycling is one of the effective methods to rejuvenate metallic glasses(MGs)and improve their mechanical properties.The anelastic origin of the rejuvenation by mechanical cycling in a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10) MG was investigated via differential scanning calorimetry(DSC)and dynamic mechanical analysis(DMA).We demonstrate that mechanical cycling promotes the activation of flow defects with short relaxation times,leading to anelastic strains and therefore considerable energy storage,which manifests itself as larger relaxation enthalpy on the DSC curves of MGs.However,the MGs release the excess relaxation enthalpy caused by anelastic strain with time,thus suppressing atomic mobility and elevating β relaxation activation energies.The strategy of mechanical cycling at small strains,as demonstrated in the current work,can expand the energy states of MGs over a wide range of relaxation enthalpies.展开更多
Structural rejuvenation is vital and attractive for modulating the energetic state and structural heterogeneity of bulk metallic glasses(BMGs). In this paper, we show that cooling a BMG from a supercooled liquid regio...Structural rejuvenation is vital and attractive for modulating the energetic state and structural heterogeneity of bulk metallic glasses(BMGs). In this paper, we show that cooling a BMG from a supercooled liquid region at laboratory rates can reverse the relaxation enthalpy lost during the preceding structural relaxation. Increasing the cooling rate is beneficial for enhancing atomic mobility and dynamic mechanical relaxation intensity. Therefore, this rejuvenation methodology promotes tailoring the mechanical properties of BMGs and provides a comprehensive understanding of the rejuvenation mechanism.展开更多
PbTiO_(3)-based piezoelectric ceramics are key materials for developing various electromechanical transduc-ers.For high-power ultrasonic transducers,piezoelectric ceramics are required to possess large piezo-electric ...PbTiO_(3)-based piezoelectric ceramics are key materials for developing various electromechanical transduc-ers.For high-power ultrasonic transducers,piezoelectric ceramics are required to possess large piezo-electric coefficient(d_(33))and high mechanical quality factor(Q_(m)).Although acceptor dopants can im-prove Q_(m),they also deteriorate d_(33).If suitable piezoelectricity-beneficial donor dopants can be intro-duced into acceptor-doped ceramics,it is very possible to obtain large d_(33)and high Q_(m)simultaneously in donor and acceptor co-doped ceramics.In this work,a series of x mol%Sm and y mol%Mn co-doped Pb(Mg_(1/3)Nb_(2/3))O_(3)-30PbTiO_(3)(PMN-30PT:x Sm,y Mn)ceramics were prepared by the solid-phase sintered method.The crystal structure,local domain structure and electromechanical properties were sys-tematically analyzed.Optimal performances were obtained in PMN-30PT:2.5Sm,1-2Mn ceramics with d_(33)=860-543 pC/N,Q_(m)=495-754,and dielectric loss tanδ=0.0055-0.0086.This high performance origi-nates from the combined effects of(Mn″Ti−V_(o)^(••))^(×)defect dipoles and the local structural heterogeneity.展开更多
In the current work,we demonstrated that the rejuvenation of metallic glasses can be achieved through training theβrelaxation process.With the increase in the training frequency,a transition from structural relaxatio...In the current work,we demonstrated that the rejuvenation of metallic glasses can be achieved through training theβrelaxation process.With the increase in the training frequency,a transition from structural relaxation to rejuvenation can be observed.This rejuvenation treatment is unexpected due to it occurs at a relatively small cyclic strain of 0.2%.Rejuvenation is beneficial to increase the relaxation enthalpy and promotes the decoupling of theβrelaxation process andαrelaxation process.A cluster ofβrelaxation time curves are formulated to describe any energetic state between ultrastable and ultimately rejuvenated metallic glasses.In addition,rejuvenation expands the distribution ofβrelaxation process,anelastic and viscoplastic components during the deformation process.展开更多
Glasses have long been considered as frozen liquids because of the similarity between their static amorphous structures.While the modern theories about glass transition suggest that glass transition may result from su...Glasses have long been considered as frozen liquids because of the similarity between their static amorphous structures.While the modern theories about glass transition suggest that glass transition may result from supercooling of a heterogeneous liquid that contains fast and slow regions,it remains unclear whether such a physical picture applies to metallic glasses,which are a densely packed solid glass that was once believed to be a vitrified homogeneous metallic liquid.However,in the recent work published in Nature Materials,Chang et al provide compelling evidence to show that metallic glasses contain liquid-like atoms that behave as a high-temperature liquid in stress relaxation.Being activated under cyclic loading,this quenched-in liquid results in a fast relaxation process,which is discovered in a variety of metallic glasses.Their results are important and deliver a strong message that metallic glasses have a dynamic microstructure containing liquid-and solid-like atoms.Most importantly,the outcome of their research provides physical insight into the nature of glass-transition in metallic glasses,and also helps unravel their structure-property relations.展开更多
Rare-earth Sm^(3+)-doped Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.25PbTiO_(3)(PMN-0.25PT)ferroelectric ceramics with doping amounts between 0%-3%were developed via a conventional solid-state method.The doping effect of Sm^(3+)ions...Rare-earth Sm^(3+)-doped Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.25PbTiO_(3)(PMN-0.25PT)ferroelectric ceramics with doping amounts between 0%-3%were developed via a conventional solid-state method.The doping effect of Sm^(3+)ions on the PMN-0.25PT matrix was systematically investigated on the basis of the phase structure,temperature-dependent dielectric,ferroelectric,and electrotechnical properties.Due to the disruption of long-range ferroelectric order,the addition of Sm^(3+)ions effectively lowers the Tm(temperature corresponding to maximum permittivity)of the samples,leading to enhanced relaxor ferroelectric(RFE)characteristic and superior electric field-induced strain(electrostrain)properties at room temperature.Intriguingly,a considerable large-signal equivalent piezoelectric coefficient d∗_(33)of 2376 pm/V and a very small hysteresis were attained in the PMN-0.25PT component doped with 2.5 mol.%Sm^(3+).The findings of piezoelectric force microscopy indicate that the addition of Sm^(3+)increases the local structural heterogeneity of the PMN-0.25PT matrix and that the enhanced electromechanical performance is due to the dynamic behavior of polar nanoregions.Importantly,strong temperature-dependent electrostrain and electrostrictive coefficient Q33 are observed in the critical region around Tm in all Sm^(3+)-modified PMN-0.25PT ceramic samples studied.This work elucidates the phase transition behavior of Sm^(3+)-doped PMN-0.25PT and reveals a critical region where electrostrictive properties can be greatly improved due to a strong temperature-dependent characteristic.展开更多
文摘In this paper, we discuss the optimal insurance in the presence of background risk while the insured is ambiguity averse and there exists belief heterogeneity between the insured and the insurer. We give the optimal insurance contract when maxing the insured’s expected utility of his/her remaining wealth under the smooth ambiguity model and the heterogeneous belief form satisfying the MHR condition. We calculate the insurance premium by using generalized Wang’s premium and also introduce a series of stochastic orders proposed by [1] to describe the relationships among the insurable risk, background risk and ambiguity parameter. We obtain the deductible insurance is the optimal insurance while they meet specific dependence structures.
文摘Ultrastable metallic glasses(SMGs)exhibit enhanced stability comparable to those of conventional glasses aged for thousands of years.The ability to understand why certain alloy compositions and processing conditions generate an SMG is an emerging challenge.Herein,amplitude-modulation dynamic atomic force microscopy was utilized for tracking the structure of Zr_(50)Cu_(50),Zr_(50)Cu_(44.5)Al_(5.5)and Zr_(50)Cu_(41.5)Al_(5.5)Mo_(3) thin film metallic glasses(TFMGs)that were produced by direct current magnetron sputtering at room temperature with the rate of deposition being the only variable.The transition in stability from bulkto SMG-like behavior resides in the change of relaxation mechanism as the deposition rate is decreased.The formation of SMGs is directly linked with the degree of structural heterogeneity,whereby MGs with greater heterogeneity have a higher potential to form SMGs with more significant enhancement in stability.Slower deposition rates,however,are required to yield the more homogenous structure and lower energy state underlying the ultrastability.Ultrastability is closely linked with the geometric shape and distribution of loosely packed phases,whereby SMGs containing more slender loosely packed phases with a more skewed distribution achieve more significant improvements in stability.This work not only provides direct evidence of the structure of SMGs,but also opens new horizons for the design of SMGs.
基金supported by the National Natural Science Foundation of China(Grant Nos.51401192 and 51611130120)the Natural Science Foundation of Shaanxi Province,China(Grant No.2016JM5009)+5 种基金the Fundamental Research Funds for the Central Universities of China(Grant Nos.3102015ZY027 and 3102015BJ(Ⅱ)JGZ019)the Aeronautical Science Foundation of China(Grant No.2015ZF53072)supported by the Hong Kong Scholar Program of China(Grant No.XJ2015056)the support of MINECO(Grant No.FIS2014-54734-P)Generalitat de Catalunya(Grant No.2014SGR00581)supported by the Research Grant Council,the Hong Kong City of China,through the General Research Fund(Grant No.City U11214914)
文摘Understanding mechanical relaxation, such as primary(α) and secondary(β) relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses. At a fundamental level, relaxation, plastic deformation, glass transition, and crystallization of metallic glasses are intimately linked to each other, which can be related to atomic packing, inter-atomic diffusion, and cooperative atom movement. Conceptually, βrelaxation is usually associated with structural heterogeneities intrinsic to metallic glasses. However, the details of such structural heterogeneities, being masked by the meta-stable disordered long-range structure, are yet to be understood. In this paper, we briefly review the recent experimental and simulation results that were attempted to elucidate structural heterogeneities in metallic glasses within the framework of β relaxation. In particular, we will discuss the correlation amongβ relaxation, structural heterogeneity, and mechanical properties of metallic glasses.
基金the Key Projects of the Yalong River Joint Fund of the National Natural Science Foundation of China(Grant No.U1865203)the Key Program of National Natural Science Foundation of China(Grant No.41931286)the China Postdoctoral Science Foundation(Grant No.2021M691147)。
文摘Due to the complex diagenesis process,basalt usually contains defects in the form of amygdales formed by diagenetic bubbles,which affect its mechanical properties.In this study,a synthetic rock mass method(SRM)based on the combination of discrete fracture network(DFN)and finite-discrete element method(FDEM)is applied to characterizing the amygdaloidal basalt,and to systematically exploring the effects of the development characteristics of amygdales and sample sizes on the mechanical properties of basalt.The results show that with increasing amygdale content,the elastic modulus(E)increases linearly,while the uniaxial compressive strength(UCS)shows an exponential or logarithmic decay.When the orientation of amygdales is between 0°and 90°,basalt shows a relatively pronounced strength and stiffness anisotropy.Based on the analysis of the geometric and mechanical properties,the representative element volume(REV)size of amygdaloidal basalt blocks is determined to be 200 mm,and the mechanical properties obtained on this scale can be regarded as the properties of the equivalent continuum.The results of this research are of value to the understanding of the mechanical properties of amygdaloidal basalt,so as to guide the formulation of engineering design schemes more accurately.
基金financially supported by the High-end Foreign Experts Recruitment Program (No. G2021163004L)the Guangdong International Science and Technology Cooperation Program (No. 2021A0505050002)+1 种基金National Key Research and Development Program of China (Nos. 2020YFB 2008300, 2020YFB2009301, and 2020YFB2008305)Guangdong Natural Science Foundation (No. 2020A1515 011242)。
文摘We report a process route to fabricate an Al–Al interpenetrating-phase composite by combining the Al–Mg–Mn–Sc–Zr lattice structure and Al_(84)Ni_(7)Gd_(6)Co_(3)nanostructured structure. The lattice structure was produced by the selective laser melting and subsequently filled with the Al_(84)Ni_(7)Gd_(6)Co_(3)amorphous powder, and finally the mixture was used for hot extrusion to produce bulk samples. The results show that the composites achieve a high densification and good interface bonding due to the element diffusion and plastic deformation during hot extrusion.The bulk samples show a heterogeneous structure with a combination of honeycomb lattice structure with an average grain size of less than1 μm and nanostructured area with a high volume fraction of nanometric intermetallics and nanograin α-Al. The heterogeneous structure leads to a bimodal mechanical zone with hard area and soft area giving rise to high strength and acceptable plasticity, where the compressive yield strength and the compressive plasticity can reach ~745 MPa and ~30%, respectively. The high strength can be explained by the rule of mixture,the grain boundary strengthening, and the back stress, while the acceptable plasticity is mainly owing to the confinement effect of the nanostructured area retarding the brittle fracture behavior.
基金the support by National Key Research and Development Program of China(2018YFA0703000)National Natural Science Foundation of China(Grant No.52105310)+1 种基金Natural Science Foundation of Zhejiang Province(Grant No.LDQ23E050001)the Starry Night Science Fund of Zhejiang University Shanghai Institute for Advanced Study(Grant No.SN-ZJU-SIAS-004)。
文摘In order to mimic the natural heterogeneity of native tissue and provide a better microenvironment for cell culturing,multi-material bioprinting has become a common solution to construct tissue models in vitro.With the embedded printing method,complex 3D structure can be printed using soft biomaterials with reasonable shape fidelity.However,the current sequential multi-material embedded printing method faces a major challenge,which is the inevitable trade-off between the printed structural integrity and printing precision.Here,we propose a simultaneous multi-material embedded printing method.With this method,we can easily print firmly attached and high-precision multilayer structures.With multiple individually controlled nozzles,different biomaterials can be precisely deposited into a single crevasse,minimizing uncontrolled squeezing and guarantees no contamination of embedding medium within the structure.We analyse the dynamics of the extruded bioink in the embedding medium both analytically and experimentally,and quantitatively evaluate the effects of printing parameters including printing speed and rheology of embedding medium,on the 3D morphology of the printed filament.We demonstrate the printing of double-layer thin-walled structures,each layer less than 200μm,as well as intestine and liver models with 5%gelatin methacryloyl that are crosslinked and extracted from the embedding medium without significant impairment or delamination.The peeling test further proves that the proposed method offers better structural integrity than conventional sequential printing methods.The proposed simultaneous multi-material embedded printing method can serve as a powerful tool to support the complex heterogeneous structure fabrication and open unique prospects for personalized medicine.
基金the National Natural Science Foundation of China(Grant Nos.11974385 and 91956101)the Fund from the Chinese Academy of Sciences(Grant No.1731300500030)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB07030100).
文摘Transport properties and the associated structural heterogeneity of room temperature aqueous ionic liquids and especially of super-concentrated electrolyte aqueous solutions have received increasing attention,due to their potential application in ionic battery.This paper briefly reviews the results reported mainly since 2010 about the liquid-liquid separation,aggregation of polar and apolar domains in neat RTILs,and solvent clusters and 3D networks chiefly constructed by anions in super-concentrated electrolyte solutions.At the same time,the dominating effect of desolvation process of metal ions at electrode/electrolyte interface upon the transport of metal ions is stressed.This paper also presents the current understanding of how water affects the anion-cation interaction,structural heterogeneities,the structure of primary coordination sheath of metal ions and consequently their transport properties in free water-poor electrolytes.
基金financially supported by the National Natural Science Foundation of China (Nos. 51971061 and 52231005)the Natural Science Foundation of Jiangsu Province (No. BK20221474)。
文摘Metallic glasses are spatially heterogeneous at the nanometer scale.However,the effects of external excitation on their structural and mechanical heterogeneity and the correlation to their properties are still unresolved.Nanoindentation,atomic force microscopy(AFM) and high-resolution transmis sion elec tron micro scopy(HRTEM) were carried out to explore the effects of cryogenic thermal cycling(CTC) on mechanical/structural heterogeneity,nano sc ale creep deformation and optical properties of nano structured metallic glass thin films(MGTFs).The results indicate that CTC treatment alters the distribution fluctuations of hardness/modulus and energy dissipation and results in an increase-then-decrease variation in mechanical heterogeneity.By applying Maxwell-Voigt model,it can be shown that CTC treatment results in a remarkable activation of more defects with longer relaxation time in soft regions but has only a slight effect on defects in hard regions.In addition,CTC treatment increases the transition time from primary-state stage to steady-state stage during creep deformation.The enhanced optical reflectivity of the MGTFs after 15 thermal cycles can be attributed to increased aggregation of Cu and Ni elements.The results of this study shed new light on understanding mechanical/structural heterogeneity and its influence on nanoscale creep deformation and optical characteristics of nanostructured MGTFs,and facilitate the design of high-performance nanostructured MGTFs.
基金supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under Award Number 5R01AR037399the UCLA Vector Core (Emmanuelle Faure and Kip Hermann) for vector and viral preparations supported by JCCC/P30 CA016042 and CURE/P30 DK41301
文摘Heterogeneous nuclear ribonucleoprotein (hnRNP) C plays a key role in RNA processing but also exerts a dominant negative effect on responses to 1,25-dihydroxyvitamin D (1,25(OH)2D) by functioning as a vitamin D response element-binding protein (VDRE-BP). hnRNPC acts a tetramer of hnRNPC1 (huC1) and hnRNPC2 (huC2), and organization of these subunits is critical to in vivo nucleic acid-binding. Overexpression of either huC1 or huC2 in human osteoblasts is sufficient to confer VDRE-BP suppression of 1,25(OH)2D-mediated transcription. However, huC1 or huC2 alone did not suppress 1,25(OH)2D-induced transcription in mouse osteoblastic cells. By contrast, overexpression of huC1 and huC2 in combination or transfection with a bone-specific polycistronic vector using a "self-cleaving" 2A peptide to co-express huC1/C2 suppressed 1,25D-mediated induction of osteoblast target gene expression. Structural diversity of hnRNPC between human/NWPs and mouse/rat/rabbit/dog was investigated by analysis of sequence variations within the hnRNP CLZ domain. The predicted loss of distal helical function in hnRNPC from lower species provides an explanation for the altered interaction between huC1/C2 and their mouse counterparts. These data provide new evidence of a role for hnRNPC1/C2 in 1,25(OH)2D-driven gene expression, and further suggest that species-specific tetramerization is a crucial determinant of its actions as a regulator of VDR-directed transactivation.
基金financially supported by the National Natural Science Foundation of China(NSFC,21805298,21905288,51904288)the Zhejiang Provincial Natural Science Foundation(Z21B030017)+2 种基金the K.C.Wong Education Foundation(GJTD-201913)the Ningbo major special projects of the Plan‘‘Science and Technology Innovation 2025”(2018B10056,2019B10046)the Ningbo 3315 Program。
文摘The retarded kinetics of oxygen evolution on electrodes is a bottleneck for electrochemical energy conversion and storage systems.NiFe-based electrocatalysts provide a cost-effective choice to confront this challenge.However,there is a lack of facile techniques for depositing compact catalytic films of high coverage and possessing a state-of-the-art performance,which is especially desired in photoelectrochemical(PEC)systems.Herein,we demonstrate a spray pyrolysis(SP)route to address this issue,featuring the kinetic selective preparation towards the desired catalytic-active material.Differing from reported SP protocols which only produce inactive oxides,this approach directly generates a unique composite film consisting of NiFe layered oxyhydroxides and amorphous oxides,exhibiting an overpotential as small as 255 mV(10 mA cm^(−2))and a turnover frequency of∼0.4 s^(−1)per metal atom.By using such a facile protocol,the surface rate-limiting issue of BiVO_(4)photoanodes can be effectively resolved,resulting in a charge injection efficiency of over 90%.Considering this deposition directly start from simple nitrates but only takes several seconds to complete,we believe it can be developed as a widely applicable and welcomed functionalization technique for diverse electrochemical devices.
基金financially supported by the National Natural Science Foundation of China (Grant No. 51871187)Department of Science and Technology of Sichuan Province (Grant No. 2020YFG0140)Fundamental Research Funds for the Central Universities (Grant No. 2682019LK04)。
文摘The heterogeneous magnesium(Mg) matrix nanocomposite with dispersed soft phase exhibits high strength and toughness. Herein, the deformation behavior and failure process were investigated to reveal the unique mechanical behavior of the heterogeneous microstructure under compression. The extensive plastic deformation is accompanied by the flattening and tilting of the soft phase, inhibiting strain localization and leading to strain hardening. Moreover, a stable crack multiplication process is activated, which endows high damage tolerance to the heterogeneous Mg matrix nanocomposites. The final failure of the composite is caused by crack coalescence in the shear plane along a tortuous path. The presence of dispersed soft phases within the hard matrix induces a noticeable change in mechanical response. Especially,the malleability of the heterogeneous Mg matrix nanocomposite is two and ten times higher than that of pure Mg and the homogeneous Mg matrix nanocomposite, respectively. The current study provides a novel strategy to break the trade-off between strength and toughness in metal matrix nanocomposites.
文摘With the rapid growth of network technology, the methods and types of cyber-attacks are increasing rapidly. Traditional static passive defense technologies focus on external security and known threats to the target system and cannot resist advanced persistent threats. To solve the situation that cyberspace security is easy to attack and difficult to defend, Chinese experts on cyberspace security proposed an innovative theory called mimic defense, it is an active defense technology that employs “Dynamic, Heterogeneous, Redundant” architecture to defense attacks. This article first briefly describes the classic network defense technology and Moving Target Defense (MTD). Next, it mainly explains in detail the principles of the mimic defense based on the DHR architecture and analyzes the attack surface of DHR architecture. This article also includes applications of mimic defense technology, such as mimic routers, and mimic web defense systems. Finally, it briefly summarizes the existing research on mimic defense, expounds the problems that need to be solved in mimic defense, and looks forward to the future development of mimic defense.
基金support provided by City University of Hong Kong (CityU) through the start-up grant for newly recruited faculty members (Project No. 7200303)the research of C.T. Liu is also supported by CityU (Project No. CityU117612)
文摘Despite the great efforts dedicated to metallic glasses (MGs), their structure still remains a mystery to be understood. With comparison to the existing mJciomechanical models, such as the free-volume and shear transformation zone (STZ) models, we first discuss in this article our recently proposed 'core-shell' model, which contains a solid-like matrix and liquid-like inclusions. This serves as the theoretical basis to understand the structural heterogeneity in MGs in our analytical framework. After that, a scanning ultrafast nanoindentation technique is used to map out the structure heterogeneity in a Zr-based bulk metallic glass (BMG). With these ongoing research efforts, we hope that more research work could be stimulated in the pursuit of the structure-property relation in MGs.
基金supported by the National Natural Science Foundation of China (Grant Nos.51971178,and 52271153)the Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(Grant No.2021JC-12)+5 种基金the Fundamental Research Funds for the Central Universities (Grant No.D5000220034)the Natural Science Foundation of Chongqing (Grant No.cstc2020jcyj-jq X0001)supported by the National Natural Science Foundation of China (Grant No.12072344)the Youth Innovation Promotion Association of the Chinese Academy of Sciencessupport from the Research Grant Council (RGC)the Hong Kong government through the General Research Fund (GRF)(Grant Nos.City U11200719,and City U11213118)
文摘Mechanical cycling is one of the effective methods to rejuvenate metallic glasses(MGs)and improve their mechanical properties.The anelastic origin of the rejuvenation by mechanical cycling in a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10) MG was investigated via differential scanning calorimetry(DSC)and dynamic mechanical analysis(DMA).We demonstrate that mechanical cycling promotes the activation of flow defects with short relaxation times,leading to anelastic strains and therefore considerable energy storage,which manifests itself as larger relaxation enthalpy on the DSC curves of MGs.However,the MGs release the excess relaxation enthalpy caused by anelastic strain with time,thus suppressing atomic mobility and elevating β relaxation activation energies.The strategy of mechanical cycling at small strains,as demonstrated in the current work,can expand the energy states of MGs over a wide range of relaxation enthalpies.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51971178 and 52271153)financially supported by National Natural Science Foundation of China (Grant No. 12072344)+4 种基金the Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(Grant No. 2021JC-12)the Natural Science Foundation of Chongqing(Grant No. cstc2020jcyj-jq X0001)sponsored by the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University (Grant No. CX2021015)the Youth Innovation Promotion Association of the Chinese Academy of Sciencesfinancial support from Research Grant Council (RGC) and the Hong Kong government through the General Research Fund (GRF)(Grant Nos.U11200719 and U11213118)。
文摘Structural rejuvenation is vital and attractive for modulating the energetic state and structural heterogeneity of bulk metallic glasses(BMGs). In this paper, we show that cooling a BMG from a supercooled liquid region at laboratory rates can reverse the relaxation enthalpy lost during the preceding structural relaxation. Increasing the cooling rate is beneficial for enhancing atomic mobility and dynamic mechanical relaxation intensity. Therefore, this rejuvenation methodology promotes tailoring the mechanical properties of BMGs and provides a comprehensive understanding of the rejuvenation mechanism.
基金This work was financially supported by the Natural Science Foundation of Heilongjiang Province(No.LH2021A012).
文摘PbTiO_(3)-based piezoelectric ceramics are key materials for developing various electromechanical transduc-ers.For high-power ultrasonic transducers,piezoelectric ceramics are required to possess large piezo-electric coefficient(d_(33))and high mechanical quality factor(Q_(m)).Although acceptor dopants can im-prove Q_(m),they also deteriorate d_(33).If suitable piezoelectricity-beneficial donor dopants can be intro-duced into acceptor-doped ceramics,it is very possible to obtain large d_(33)and high Q_(m)simultaneously in donor and acceptor co-doped ceramics.In this work,a series of x mol%Sm and y mol%Mn co-doped Pb(Mg_(1/3)Nb_(2/3))O_(3)-30PbTiO_(3)(PMN-30PT:x Sm,y Mn)ceramics were prepared by the solid-phase sintered method.The crystal structure,local domain structure and electromechanical properties were sys-tematically analyzed.Optimal performances were obtained in PMN-30PT:2.5Sm,1-2Mn ceramics with d_(33)=860-543 pC/N,Q_(m)=495-754,and dielectric loss tanδ=0.0055-0.0086.This high performance origi-nates from the combined effects of(Mn″Ti−V_(o)^(••))^(×)defect dipoles and the local structural heterogeneity.
基金supported by the NSFC(Grant Nos.51971178 and 52271153)the Natural Science Basic Research Plan for Distin-guished Young Scholars in Shaanxi Province(Grant No.2021JC-12)+5 种基金Fundamental Research Funds for the Central Universities(Grant No.D5000220034)the Natural Science Foundation of Chongqing(Grant No.cstc2020jcyj-jqX0001)financially supported by NSFC(Grant No.12072344)the Youth Innovation Promo-tion Association of the Chinese Academy of Sciencesfinancial support from Research Grant Council(RGC)the Hong Kong government through the General Research Fund(GRF)with Grant Nos.CityU11200719 and CityU11213118.
文摘In the current work,we demonstrated that the rejuvenation of metallic glasses can be achieved through training theβrelaxation process.With the increase in the training frequency,a transition from structural relaxation to rejuvenation can be observed.This rejuvenation treatment is unexpected due to it occurs at a relatively small cyclic strain of 0.2%.Rejuvenation is beneficial to increase the relaxation enthalpy and promotes the decoupling of theβrelaxation process andαrelaxation process.A cluster ofβrelaxation time curves are formulated to describe any energetic state between ultrastable and ultimately rejuvenated metallic glasses.In addition,rejuvenation expands the distribution ofβrelaxation process,anelastic and viscoplastic components during the deformation process.
基金the financial support provided by Research Grants Council,the Hong Kong government through the General Research Fund(Grant Nos.CityU11200719 and CityU11213118)the City University of Hong Kong through CityU Strategic Research Grant(Grant No.7005438)+1 种基金Q W acknowledges the financial support provided by Natural Science Foundation of China(Grant Nos.52171161,51871140)the space utilization system of China Manned Space Engineering(KJZ-YY-NCL08).
文摘Glasses have long been considered as frozen liquids because of the similarity between their static amorphous structures.While the modern theories about glass transition suggest that glass transition may result from supercooling of a heterogeneous liquid that contains fast and slow regions,it remains unclear whether such a physical picture applies to metallic glasses,which are a densely packed solid glass that was once believed to be a vitrified homogeneous metallic liquid.However,in the recent work published in Nature Materials,Chang et al provide compelling evidence to show that metallic glasses contain liquid-like atoms that behave as a high-temperature liquid in stress relaxation.Being activated under cyclic loading,this quenched-in liquid results in a fast relaxation process,which is discovered in a variety of metallic glasses.Their results are important and deliver a strong message that metallic glasses have a dynamic microstructure containing liquid-and solid-like atoms.Most importantly,the outcome of their research provides physical insight into the nature of glass-transition in metallic glasses,and also helps unravel their structure-property relations.
基金the National Natural Science Foundation of China(Grant No.52261135548)the Key Research and Development Program of Shaanxi(Program No.2022KWZ-22)+3 种基金the National Key Research and Development Program of China(Grant Nos.2021YFE0115000 and 2021YFB3800602)Russian Science Foundation(Project No.23-42-00116)the Ural Center for Shared Use“Modern nanotechnology”Ural Federal University(Reg.No.2968)which is supported by the Ministry of Science and Higher Education RF(Project No.075-15-2021-677)was used.The SEM work was done at International Center for Dielectric Research(ICDR),Xi’an Jiaotong University,Xi’an,China.
文摘Rare-earth Sm^(3+)-doped Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.25PbTiO_(3)(PMN-0.25PT)ferroelectric ceramics with doping amounts between 0%-3%were developed via a conventional solid-state method.The doping effect of Sm^(3+)ions on the PMN-0.25PT matrix was systematically investigated on the basis of the phase structure,temperature-dependent dielectric,ferroelectric,and electrotechnical properties.Due to the disruption of long-range ferroelectric order,the addition of Sm^(3+)ions effectively lowers the Tm(temperature corresponding to maximum permittivity)of the samples,leading to enhanced relaxor ferroelectric(RFE)characteristic and superior electric field-induced strain(electrostrain)properties at room temperature.Intriguingly,a considerable large-signal equivalent piezoelectric coefficient d∗_(33)of 2376 pm/V and a very small hysteresis were attained in the PMN-0.25PT component doped with 2.5 mol.%Sm^(3+).The findings of piezoelectric force microscopy indicate that the addition of Sm^(3+)increases the local structural heterogeneity of the PMN-0.25PT matrix and that the enhanced electromechanical performance is due to the dynamic behavior of polar nanoregions.Importantly,strong temperature-dependent electrostrain and electrostrictive coefficient Q33 are observed in the critical region around Tm in all Sm^(3+)-modified PMN-0.25PT ceramic samples studied.This work elucidates the phase transition behavior of Sm^(3+)-doped PMN-0.25PT and reveals a critical region where electrostrictive properties can be greatly improved due to a strong temperature-dependent characteristic.