In the era of the digital economy,digital trade has demonstrated strong vitality,becoming a crucial driving force for the highquality development of national and regional economies.However,understanding the resilience...In the era of the digital economy,digital trade has demonstrated strong vitality,becoming a crucial driving force for the highquality development of national and regional economies.However,understanding the resilience of digital trade in the face of external crises is an important topic.Taking the backdrop of Sino-US trade friction,this paper constructs a resilience index system for digital trade.It utilizes entropy method,kernel density estimation,and ArcGIS mapping to calculate and visually analyze the resilience of China’s digital trade from 2017 to 2021.Additionally,a Tobit model is constructed to explore the main influencing factors of digital trade resilience patterns.The research findings indicate:1)temporally,during the period of Sino-US trade friction,China’s digital trade resilience shows an overall upward trend,but there are regional differences in resilience levels across the country,with a severe polarization phenomenon.2)Spatially,high resilience is observed in the eastern and central regions of China,while the western and northeastern regions exhibit low resilience.3)From a dimensional perspective,the resistance of digital trade resilience displays a spatial distribution of high values in the east and low values in the west.The recovery force is aggregated along coastal areas,and the renewal force tends to aggregate along the eastern coastline.4)Factors such as economic scale,industrial structure,urbanization rate,government fiscal expenditure,and technological talents significantly promote the enhancement of digital trade resilience.This study reveals the dynamic characteristics and influencing factors of digital trade resilience in responding to external shocks,providing theoretical basis and policy suggestions for enhancing digital trade resilience,and promoting high-quality economic development in China.展开更多
Transonic shocks play a pivotal role in designation of supersonic inlets and ramjets.For the three-dimensional steady non-isentropic compressible Euler system with frictions,we constructe a family of transonic shock s...Transonic shocks play a pivotal role in designation of supersonic inlets and ramjets.For the three-dimensional steady non-isentropic compressible Euler system with frictions,we constructe a family of transonic shock solutions in rectilinear ducts with square cross-sections.In this article,we are devoted to proving rigorously that a large class of these transonic shock solutions are stable,under multidimensional small perturbations of the upcoming supersonic flows and back pressures at the exits of ducts in suitable function spaces.This manifests that frictions have a stabilization effect on transonic shocks in ducts,in consideration of previous works which shown that transonic shocks in purely steady Euler flows are not stable in such ducts.Except its implications to applications,because frictions lead to a stronger coupling between the elliptic and hyperbolic parts of the three-dimensional steady subsonic Euler system,we develop the framework established in previous works to study more complex and interesting Venttsel problems of nonlocal elliptic equations.展开更多
“China will fight to the end if the United States continues to escalate trade frictions,”the Ministry of Commerce(MOC)said recently.China will not give ground on issues of principle during bilateral economic and tra...“China will fight to the end if the United States continues to escalate trade frictions,”the Ministry of Commerce(MOC)said recently.China will not give ground on issues of principle during bilateral economic and trade talks,which are clearly stated in a white paper on bilateral trade consultations issued earlier this month,MOC spokesperson Gao Feng said.In response to the new threat of tarrifs by the United States,Gao said China is firmly against US unilateralism and bullying.展开更多
Human society is ,no stranger to risk,but the global challenges and security threats faced by the world today make risk management or crisis control more inevitable in social and national governance.The goal of crisis...Human society is ,no stranger to risk,but the global challenges and security threats faced by the world today make risk management or crisis control more inevitable in social and national governance.The goal of crisis management is to overcome differences,build trust,reduce or eliminate conflict risk and keep the overall layout as normal.Crisis control, as well as economic construction,the legislative agenda,and social mechanisms are two sides of national governance.Against the backdrop of the expansion of China-US exchanges and communication and China's rising strength and global influence,there have been many political, economic and military frictions between China and the United States.展开更多
THE ongoing China-U.S. trade frictions have raised foreign investors’ concerns over China’s macroeconomic prospects, possible restrictions on U.S. companies, and a damper on its business climate. However, numbers sp...THE ongoing China-U.S. trade frictions have raised foreign investors’ concerns over China’s macroeconomic prospects, possible restrictions on U.S. companies, and a damper on its business climate. However, numbers speak louder than words. In 2018, foreign direct investment (FDI) in China went up against the global investment outlook, refuting the rhetoric that foreign companies are pulling out of the Chinese market as the U.S. slaps tariffs on Chinese goods.展开更多
International portfolio management is influenced by the existence of“frictions”,factors or events that interfere with trade,which are linked in financial literature to market-specific factors,such as available infor...International portfolio management is influenced by the existence of“frictions”,factors or events that interfere with trade,which are linked in financial literature to market-specific factors,such as available information,restrictions,investor protection,or market liquidity.Given the wide variety of factors that can be included in these categories,scientific studies typically focus on a reduced number of indicators at a time in order to offer an in depth analysis of their impact.We offer a consolidated view of the perspectives observed in financial literature by proposing a novel index for market frictions that includes all these four components and rank fifteen post-communist East European capital markets based on their index values.We then constructed various scenarios by assuming different levels of importance for the criteria used in index construction.By employing grey clustering analysis,we cluster these capital markets into three categories—strongly recommended,recommended with some reserve,and not recommended—based on the importance given by the decision maker to these factors.The results show that some of the studied markets are in the same cluster,irrespective of the chosen scenario.The only market always included in the“strongly recommended”category is Hungary,indicating that it is a good investment option for international participants.Bulgaria and Slovakia are always regarded as“recommended with reserve”markets,whereas the Republic of Moldova is part of the“not recommended”category.The other markets show a degree of variability that can be explained by different investor perspectives.This study contributes to the existing literature by combining the advantages of grey clustering and portfolio analysis.Investors can use this approach during the decision-making process related to their investments.展开更多
The effects of welding speed on the macroscopic and microscopic residual stresses(RSes) in friction stir welded 17 vol.% SiCp/2009 Al-T4 composite plates were studied via neutron diffraction and an improved decoupled ...The effects of welding speed on the macroscopic and microscopic residual stresses(RSes) in friction stir welded 17 vol.% SiCp/2009 Al-T4 composite plates were studied via neutron diffraction and an improved decoupled hierarchical multiscale modeling methods. Measurements showed that the macroscopic and total RSes had the largest variations in the longitudinal direction(LD). Increasing the welding speed led to higher values of measured LD macroscopic and total RSes in the matrix. The welding speed also significantly influenced the distributions and magnitudes of the microscopic RSes. The RSes were predicted via an improved hierarchical multiscale model, which includes a constant coefficient of friction based thermal model. The RSes in the composite plates before friction stir welding(FSW) were computed and then set as the initial states of the FSW process during modeling. This improved decoupled multiscale model provided improved predictions of the temperature and RSes compared with our previous model.展开更多
It is shown that the activation energy spectrum of hydrogen in amorphous materials can be determined from the temperature distribution of internal friction observed in anelastic relaxation measurements by using the de...It is shown that the activation energy spectrum of hydrogen in amorphous materials can be determined from the temperature distribution of internal friction observed in anelastic relaxation measurements by using the deconvolution method of Fourier transform.展开更多
Choices of excitation signals are important in engineering sciences and in physical simulations;a sufficient excitation can be critical in modelling a complicated nonlinear dynamic system. The discontinuous dynamic of...Choices of excitation signals are important in engineering sciences and in physical simulations;a sufficient excitation can be critical in modelling a complicated nonlinear dynamic system. The discontinuous dynamic of a non-linear, friction-induced with two idealized periodical forced oscillators is studied. The dry friction in the system follows the classical Coulomb law, and various friction characteristics of dry friction laws in engineering sciences. To capture the presence of the two driving forces, the system must be studied as a function of their frequency-modulated and its equivalent amplitude modulated waveforms. Our numerical investigation shows a rich dynamical behaviour including periodic, quasi-periodic motions, thus a variable dynamics phenomenon among others;such as modulated waves, modulated stick-slip, periodic oscillation, and periodic stick-slip. It seems that such excitation forces can be used to conveniently identify the existence of nonlinearity, dry friction effects, and strength degradation in the system. The results achieved via the Coulomb’s law are compared with those obtained via two others particular friction laws: the complete model with Stribeck effect and Coulomb viscosity.展开更多
When China announced that it would “seal customs operations” in Hainan,the phrase travelled poorly beyond its borders. To many foreign readers, the term sounds defensive, even restrictive—as if an island were being...When China announced that it would “seal customs operations” in Hainan,the phrase travelled poorly beyond its borders. To many foreign readers, the term sounds defensive, even restrictive—as if an island were being closed off at a time when the global economy urgently needs openness.From Southeast Asia, however, the policy looks less like retreat and more like revelation.It shines light on how China’s understanding of openness has evolved—shaped not by slogans, but by the trade frictions of recent years. What is unfolding in Hainan is not an attempt to close an island, but an effort to define,with unusual precision, where openness begins and how it is sustained.展开更多
Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing addit...Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing additive-induced defects,and alleviating residual stress and deformation,all of which are critical for enhancing the mechanical performance of the manufactured parts.Integrating interlayer friction stir processing(FSP)into WAAM significantly enhances the quality of deposited materials.However,numerical simulation research focusing on elucidating the associated thermomechanical coupling mechanisms remains insufficient.A comprehensive numerical model was developed to simulate the thermomechanical coupling behavior in friction stir-assisted WAAM.The influence of post-deposition FSP on the coupled thermomechanical response of the WAAM process was analyzed quantitatively.Moreover,the residual stress distribution and deformation behavior under both single-layer and multilayer deposition conditions were investigated.Thermal analysis of different deposition layers in WAAM and friction stir-assisted WAAM was conducted.Results show that subsequent layer deposition induces partial remelting of the previously solidified layer,whereas FSP does not cause such remelting.Furthermore,thermal stress and deformation analysis confirm that interlayer FSP effectively mitigates residual stresses and distortion in WAAM components,thereby improving their structural integrity and mechanical properties.展开更多
Isolation technology can reduce the type of structural damage that earthquakes cause.A new type of composite sliding-rolling friction composite seismic isolation bearing(SRF)with composite sliding friction and rolling...Isolation technology can reduce the type of structural damage that earthquakes cause.A new type of composite sliding-rolling friction composite seismic isolation bearing(SRF)with composite sliding friction and rolling friction is proposed.SRF is capable of realizing a parallel arrangement of sliding friction and rolling friction,and the coefficient of dynamic friction shows variability.The proposed static tests on composite bearings were conducted to investigate the effects of the number of shims,loading speed and vertical pressure on the dynamic friction factor.Test results show that the coefficient of dynamic friction first generally decreases and then increases with an increase in sliding speed,prior to again decreasing with an increase in vertical pressure.The dynamic friction factor increases and then decreases with an increase in the number of shims for a four-roll ball.It decreases and then increases with an increase in the number of shims for a five-roll ball.Based on finite element analysis,modeling and analyzing the effects of the coefficient of friction,the number of balls and the number of shims on the hysteresis performance of the support and derive its skeleton curve.The SRF hysteretic performance,dynamic friction factor and the number of rolling balls and shims show significant correlation.展开更多
The failure of liquid storage tanks,one of the most critical infrastructure systems widely used,during severe earthquakes can have direct or indirect impacts on public safety.The significance of their safe performance...The failure of liquid storage tanks,one of the most critical infrastructure systems widely used,during severe earthquakes can have direct or indirect impacts on public safety.The significance of their safe performance even after destructive earthquakes and their potential for operational use underscores the necessity of appropriate seismic design.Hence,seismic isolation,specifically base isolation,has gained attention as a seismic control method to reduce damage to these infrastructures by increasing their vibration period.One prevalent type of seismic isolator used for tanks and other structures is the friction pendulum system(FPS)isolator.However,due to its fixed period or frequency,it may be susceptible to resonance effects during long-period earthquakes.This research explores an alternative solution by investigating the variable-curvature friction pendulum isolator(VFPI).This isolator type exhibits behavior similar to that of FPS isolators under low excitations and transforms into a pure friction system under high excitations.The study proposes optimizing this VFPI,which features a polynomial function termed the Polynomial Friction Pendulum Isolator(PFPI),by introducing a suitable optimization function to minimize the acceleration transmitted to the superstructure,thereby improving the dynamic performance of the elevated storage tank.The research utilizes two wellestablished metaheuristic algorithms for optimization.It evaluates the effectiveness of the proposed isolator through time history analysis using the state space procedure under various ground motion records.Results,particularly under long-period ground motions,indicate a substantial reduction in the dynamic response of an elevated liquid storage tank equipped with the optimized PFPI.This underscores the potential of the proposed solution in enhancing the seismic resilience of liquid storage tanks.展开更多
Turbulent flow over gravel beds in open channels is a fundamental yet complex problem in hydraulic engineering,as flow behavior is highly sensitive to channel geometry and bed roughness.In this study,the Volume of Flu...Turbulent flow over gravel beds in open channels is a fundamental yet complex problem in hydraulic engineering,as flow behavior is highly sensitive to channel geometry and bed roughness.In this study,the Volume of Fluid(VOF)method coupled with the standard k-εturbulence model is employed to simulate air-water interactions over gravel beds,with open boundary conditions capturing realistic channel-atmosphere interactions.Numerical simulations are performed to examine how channel design influences the relationship between the friction factor(f)and the Reynolds number(RN).Velocity and VOF contours indicate peak flow near the inlet,with a maximum velocity of 0.64 m/s.The simulations show strong agreement with theoretical predictions,yielding a correlation coefficient of 0.99 for RN,while f and Chezy’s coefficient(C)reach 0.75 and 0.71,respectively.Comparison with experimental measurements shows deviations of approximately 17% for RN,25% for f,and 12% for C.Moreover,further analysis confirms an inverse linear relationship between f and RN,in accordance with classical models such as Bazin’s curves,the Colebrook equation,and Moody’s approximation.Overall,the results demonstrate that the proposed numerical framework reliably captures flow dynamics over gravel beds,offering a robust tool for hydraulic design and performance assessment of open channels.展开更多
Pain,as a common symptom,seriously affects the patient's health.The aim of this work was to study the physiological responses of the brain and identify the features of Electroencephalography(EEG)signals related to...Pain,as a common symptom,seriously affects the patient's health.The aim of this work was to study the physiological responses of the brain and identify the features of Electroencephalography(EEG)signals related to friction pain.The results showed that the primary brain activation evoked by friction pain was located in the Prefrontal Cortex(PFC).The activation area decreased,and the negative activation intensity in the PFC region increased with increasing intensity of pain.The inhibitory interactions between different brain regions,especially between the PFC and primary somatosensory cortex(SI)regions were enhanced,and excitatory-inhibitory connections between the medial and lateral pain pathways were balanced during pain perception.The percentage power spectral density of theαrhythm(Dα),dominant singularity strength(αpeak)and longest vertical line(Vmax)of EEG signals induced by pain significantly decreased,and the percent-age power spectral density of theβrhythm(Dβ)significantly increased.The combination of multiple features of Dα,Dβ,αpeak and Vmax could significantly improve the average recognition accuracy of different pain states.This study elucidated the neural processing mechanisms of friction-induced pain,and EEG features associated with friction pain were extracted and recognized.It was helpful to study the brain feedback mechanisms of pain and control signals of Brain-Computer Interface(BCI)system related to pain.展开更多
UHMWPE(Ultra-High Molecular Weight Polyethylene)plain-weave fabric,characterized by its lightweight and high-strength properties,is widely used in protective equipment such as bulletproof vests and stab-resistant vest...UHMWPE(Ultra-High Molecular Weight Polyethylene)plain-weave fabric,characterized by its lightweight and high-strength properties,is widely used in protective equipment such as bulletproof vests and stab-resistant vests,serving as a key material for enhancing protective performance.This study systematically investigates the influence mechanism of interfacial properties on the energy absorption characteristics of UHMWPE-based protective structures through multi-scale experiments and numerical simulations,and establishes a cross-scale design methodology.Innovatively,an orthotropic constitutive model incorporating dynamic friction coefficients is constructed,combined with a modified Johnson-Cook failure criterion,to achieve high-precision simulation of the entire ballistic impact process(error<3.5%).Additionally,a friction field prediction model considering strain rate effects is developed,and the friction evolution laws of UHMWPE and Para-aramid(Kevlar)fabrics under strain rates of 10^(−3) and 10^(−4) s^(−1) are obtained through MTS pull-out tests.The results show that:(1)there exists a critical yarn-yarn friction coefficient(μ=0.2);exceeding this value leads to a 19%reduction in energy absorption capacity,while viscous interfaces increase the energy dissipation peak by 16%;(2)UHMWPE shows kinetically-dominated absorption(58%)with high rate but high load,increasing damage risk.Para-aramid has friction-dominated absorption(53%)with a lower rate but stable load.Hybrid fabrics use potential-dominated absorption(49%)at a moderate rate,balancing stability and protection.(3)3–5 layers of UHMWPE fabric yield optimal cost-effectiveness,with the unit cost reduction rate of the HS+5U scheme reaching 2.74 m/(s·$),which is 91%higher than that of the hybrid scheme.(4)For HS+5U(5-ply UHMWPE),V50 is 520 m/s,meeting primary protection requirement.For hybrid solutions with U/K≥3(e.g.,HS+6U+2K),V50 reaches 580 m/s(≥540 m/s),satisfying advanced protection requirement.This research provides critical references for the design of flexible protective structures and their engineering applications.展开更多
To solve the problem of abnormal abrasion of Cu-Based Friction Materials(CBFMs),Bionic Non-Smooth Surface(BNS)on friction surface of CBFMs was constructed based on bionic principles,and the optimal bionic prototype wa...To solve the problem of abnormal abrasion of Cu-Based Friction Materials(CBFMs),Bionic Non-Smooth Surface(BNS)on friction surface of CBFMs was constructed based on bionic principles,and the optimal bionic prototype was selected by Finite Element Method(FEM).In addition,the bionic parameters were optimized by Response Surface Method(RSM).Samples holding BNS were prepared by Laser Processing,tribological properties were tested by a Friction and Wear Tester and worn surface morphology was characterized by a Scanning Electron Microscope(SEM).The results showed that BNS on friction surface could regulate the stress distribution and alleviate the peak stress.Among all samples,the coupled texture of pit-hexagonal got the minimum peak stress.During braking,bionic texture could also collect wear debris or change the motion forms from sliding to rotation,which can reduce abnormal abrasion.The wear rate was reduced by 19.31%.The results in this paper can provide a new idea for enhancing the tribological properties of CBFMs,and can also lay the foundation for further research of bionic tribology.展开更多
In this paper,our main goal is to study a new mathematical model which describes the frictional contact between a foundation and a deformable body which is composed of viscoplastic materials and where the process is c...In this paper,our main goal is to study a new mathematical model which describes the frictional contact between a foundation and a deformable body which is composed of viscoplastic materials and where the process is considered dynamic.The contact condition on the normal plane is modeled by a unilateral constraint condition for a version of normal velocity in which the memory effect and the adhesion are considered.On the tangential plane a frictional contact condition is governed by the Clarke subdifferential of a locally Lipschitz function,and the evolution of the bonding field is governed by an ordinary differential equation.We formulate this problem as coupled system that consists of two ordinary differential equations and a variational-hemivariational inequality.Then,the existence,uniqueness and continuous dependence of the solution on the data results concerning the abstract system are established.Finally,we use the abstract results to show the existence and uniqueness of the solution to the contact problem.展开更多
Ion-exchange Polymer-Metal Composites(IPMCs)gain huge attentions due to large deformation,rapid electromechanical response,and high energy conversion efficiency.Deflection of IPMC arises from the volumetric swelling e...Ion-exchange Polymer-Metal Composites(IPMCs)gain huge attentions due to large deformation,rapid electromechanical response,and high energy conversion efficiency.Deflection of IPMC arises from the volumetric swelling effect induced by the concentration gradient of hydrated cations between the two electrodes,thus the volume of hydrated cation deter-mines the motion magnitude and direction of IPMC.H ion is one of the most commonly used driving cations for IPMC.However,due to its unique characteristics,particularly the inability to accurately quantify its hydration volume,existing literatures primarily focus on the physical driving models for metallic cations,i.e.,Na+,no driving model for the H ion is reported until now.This paper proposes a novel model of H ion escape from the water's body-centered cubic lattice to count the hydration volume.Number(n)of water molecules carried by the H ion is solved by combining the Lennard-Jones potential energy function with Maxwell's velocity distribution.The specific n value is equivalent to 4.04 for the H ion inside Nafion electrolyte under a 3.0 V DC electric field.Substituting it into the classic Friction Model(proposed by Tadokoro et al.at 2000),actuation behaviors of H ion driven IPMC were therefore achieved through Matlab calculations and Abaqus simulations.The calculated results of dynamic displacement and force highly match to the experimental data form the Nafion IPMC actuator driven by same electric field,showing a highly reliability of the established escape model.展开更多
基金Under the auspices of National Natural Science Foundation of China(No.42471205)the General Scientific Research Project of Zhejiang Provincial Department of Education(No.2024JYTYB12)the Philosophy and Social Science Planning Project of Zhejiang Province(No.23NDJC109YB)。
文摘In the era of the digital economy,digital trade has demonstrated strong vitality,becoming a crucial driving force for the highquality development of national and regional economies.However,understanding the resilience of digital trade in the face of external crises is an important topic.Taking the backdrop of Sino-US trade friction,this paper constructs a resilience index system for digital trade.It utilizes entropy method,kernel density estimation,and ArcGIS mapping to calculate and visually analyze the resilience of China’s digital trade from 2017 to 2021.Additionally,a Tobit model is constructed to explore the main influencing factors of digital trade resilience patterns.The research findings indicate:1)temporally,during the period of Sino-US trade friction,China’s digital trade resilience shows an overall upward trend,but there are regional differences in resilience levels across the country,with a severe polarization phenomenon.2)Spatially,high resilience is observed in the eastern and central regions of China,while the western and northeastern regions exhibit low resilience.3)From a dimensional perspective,the resistance of digital trade resilience displays a spatial distribution of high values in the east and low values in the west.The recovery force is aggregated along coastal areas,and the renewal force tends to aggregate along the eastern coastline.4)Factors such as economic scale,industrial structure,urbanization rate,government fiscal expenditure,and technological talents significantly promote the enhancement of digital trade resilience.This study reveals the dynamic characteristics and influencing factors of digital trade resilience in responding to external shocks,providing theoretical basis and policy suggestions for enhancing digital trade resilience,and promoting high-quality economic development in China.
基金This work was supported in part by National Nature Science Foundation of China(11371141 and 11871218)by Science and Technology Commission of Shanghai Municipality(18dz2271000).
文摘Transonic shocks play a pivotal role in designation of supersonic inlets and ramjets.For the three-dimensional steady non-isentropic compressible Euler system with frictions,we constructe a family of transonic shock solutions in rectilinear ducts with square cross-sections.In this article,we are devoted to proving rigorously that a large class of these transonic shock solutions are stable,under multidimensional small perturbations of the upcoming supersonic flows and back pressures at the exits of ducts in suitable function spaces.This manifests that frictions have a stabilization effect on transonic shocks in ducts,in consideration of previous works which shown that transonic shocks in purely steady Euler flows are not stable in such ducts.Except its implications to applications,because frictions lead to a stronger coupling between the elliptic and hyperbolic parts of the three-dimensional steady subsonic Euler system,we develop the framework established in previous works to study more complex and interesting Venttsel problems of nonlocal elliptic equations.
文摘“China will fight to the end if the United States continues to escalate trade frictions,”the Ministry of Commerce(MOC)said recently.China will not give ground on issues of principle during bilateral economic and trade talks,which are clearly stated in a white paper on bilateral trade consultations issued earlier this month,MOC spokesperson Gao Feng said.In response to the new threat of tarrifs by the United States,Gao said China is firmly against US unilateralism and bullying.
文摘Human society is ,no stranger to risk,but the global challenges and security threats faced by the world today make risk management or crisis control more inevitable in social and national governance.The goal of crisis management is to overcome differences,build trust,reduce or eliminate conflict risk and keep the overall layout as normal.Crisis control, as well as economic construction,the legislative agenda,and social mechanisms are two sides of national governance.Against the backdrop of the expansion of China-US exchanges and communication and China's rising strength and global influence,there have been many political, economic and military frictions between China and the United States.
文摘THE ongoing China-U.S. trade frictions have raised foreign investors’ concerns over China’s macroeconomic prospects, possible restrictions on U.S. companies, and a damper on its business climate. However, numbers speak louder than words. In 2018, foreign direct investment (FDI) in China went up against the global investment outlook, refuting the rhetoric that foreign companies are pulling out of the Chinese market as the U.S. slaps tariffs on Chinese goods.
文摘International portfolio management is influenced by the existence of“frictions”,factors or events that interfere with trade,which are linked in financial literature to market-specific factors,such as available information,restrictions,investor protection,or market liquidity.Given the wide variety of factors that can be included in these categories,scientific studies typically focus on a reduced number of indicators at a time in order to offer an in depth analysis of their impact.We offer a consolidated view of the perspectives observed in financial literature by proposing a novel index for market frictions that includes all these four components and rank fifteen post-communist East European capital markets based on their index values.We then constructed various scenarios by assuming different levels of importance for the criteria used in index construction.By employing grey clustering analysis,we cluster these capital markets into three categories—strongly recommended,recommended with some reserve,and not recommended—based on the importance given by the decision maker to these factors.The results show that some of the studied markets are in the same cluster,irrespective of the chosen scenario.The only market always included in the“strongly recommended”category is Hungary,indicating that it is a good investment option for international participants.Bulgaria and Slovakia are always regarded as“recommended with reserve”markets,whereas the Republic of Moldova is part of the“not recommended”category.The other markets show a degree of variability that can be explained by different investor perspectives.This study contributes to the existing literature by combining the advantages of grey clustering and portfolio analysis.Investors can use this approach during the decision-making process related to their investments.
基金supported financially by the National Key R&D Program of China (No. 2017YFB0703104)the National Natural Science Foundation of China (No. 51401219)
文摘The effects of welding speed on the macroscopic and microscopic residual stresses(RSes) in friction stir welded 17 vol.% SiCp/2009 Al-T4 composite plates were studied via neutron diffraction and an improved decoupled hierarchical multiscale modeling methods. Measurements showed that the macroscopic and total RSes had the largest variations in the longitudinal direction(LD). Increasing the welding speed led to higher values of measured LD macroscopic and total RSes in the matrix. The welding speed also significantly influenced the distributions and magnitudes of the microscopic RSes. The RSes were predicted via an improved hierarchical multiscale model, which includes a constant coefficient of friction based thermal model. The RSes in the composite plates before friction stir welding(FSW) were computed and then set as the initial states of the FSW process during modeling. This improved decoupled multiscale model provided improved predictions of the temperature and RSes compared with our previous model.
基金Supported partly by the National Natural Science Foundation of Chinapartly by the National Committee of Advanced Materials of China.
文摘It is shown that the activation energy spectrum of hydrogen in amorphous materials can be determined from the temperature distribution of internal friction observed in anelastic relaxation measurements by using the deconvolution method of Fourier transform.
文摘Choices of excitation signals are important in engineering sciences and in physical simulations;a sufficient excitation can be critical in modelling a complicated nonlinear dynamic system. The discontinuous dynamic of a non-linear, friction-induced with two idealized periodical forced oscillators is studied. The dry friction in the system follows the classical Coulomb law, and various friction characteristics of dry friction laws in engineering sciences. To capture the presence of the two driving forces, the system must be studied as a function of their frequency-modulated and its equivalent amplitude modulated waveforms. Our numerical investigation shows a rich dynamical behaviour including periodic, quasi-periodic motions, thus a variable dynamics phenomenon among others;such as modulated waves, modulated stick-slip, periodic oscillation, and periodic stick-slip. It seems that such excitation forces can be used to conveniently identify the existence of nonlinearity, dry friction effects, and strength degradation in the system. The results achieved via the Coulomb’s law are compared with those obtained via two others particular friction laws: the complete model with Stribeck effect and Coulomb viscosity.
文摘When China announced that it would “seal customs operations” in Hainan,the phrase travelled poorly beyond its borders. To many foreign readers, the term sounds defensive, even restrictive—as if an island were being closed off at a time when the global economy urgently needs openness.From Southeast Asia, however, the policy looks less like retreat and more like revelation.It shines light on how China’s understanding of openness has evolved—shaped not by slogans, but by the trade frictions of recent years. What is unfolding in Hainan is not an attempt to close an island, but an effort to define,with unusual precision, where openness begins and how it is sustained.
基金National Key Research and Development Program of China(2022YFB4600902)Shandong Provincial Science Foundation for Outstanding Young Scholars(ZR2024YQ020)。
文摘Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing additive-induced defects,and alleviating residual stress and deformation,all of which are critical for enhancing the mechanical performance of the manufactured parts.Integrating interlayer friction stir processing(FSP)into WAAM significantly enhances the quality of deposited materials.However,numerical simulation research focusing on elucidating the associated thermomechanical coupling mechanisms remains insufficient.A comprehensive numerical model was developed to simulate the thermomechanical coupling behavior in friction stir-assisted WAAM.The influence of post-deposition FSP on the coupled thermomechanical response of the WAAM process was analyzed quantitatively.Moreover,the residual stress distribution and deformation behavior under both single-layer and multilayer deposition conditions were investigated.Thermal analysis of different deposition layers in WAAM and friction stir-assisted WAAM was conducted.Results show that subsequent layer deposition induces partial remelting of the previously solidified layer,whereas FSP does not cause such remelting.Furthermore,thermal stress and deformation analysis confirm that interlayer FSP effectively mitigates residual stresses and distortion in WAAM components,thereby improving their structural integrity and mechanical properties.
文摘Isolation technology can reduce the type of structural damage that earthquakes cause.A new type of composite sliding-rolling friction composite seismic isolation bearing(SRF)with composite sliding friction and rolling friction is proposed.SRF is capable of realizing a parallel arrangement of sliding friction and rolling friction,and the coefficient of dynamic friction shows variability.The proposed static tests on composite bearings were conducted to investigate the effects of the number of shims,loading speed and vertical pressure on the dynamic friction factor.Test results show that the coefficient of dynamic friction first generally decreases and then increases with an increase in sliding speed,prior to again decreasing with an increase in vertical pressure.The dynamic friction factor increases and then decreases with an increase in the number of shims for a four-roll ball.It decreases and then increases with an increase in the number of shims for a five-roll ball.Based on finite element analysis,modeling and analyzing the effects of the coefficient of friction,the number of balls and the number of shims on the hysteresis performance of the support and derive its skeleton curve.The SRF hysteretic performance,dynamic friction factor and the number of rolling balls and shims show significant correlation.
文摘The failure of liquid storage tanks,one of the most critical infrastructure systems widely used,during severe earthquakes can have direct or indirect impacts on public safety.The significance of their safe performance even after destructive earthquakes and their potential for operational use underscores the necessity of appropriate seismic design.Hence,seismic isolation,specifically base isolation,has gained attention as a seismic control method to reduce damage to these infrastructures by increasing their vibration period.One prevalent type of seismic isolator used for tanks and other structures is the friction pendulum system(FPS)isolator.However,due to its fixed period or frequency,it may be susceptible to resonance effects during long-period earthquakes.This research explores an alternative solution by investigating the variable-curvature friction pendulum isolator(VFPI).This isolator type exhibits behavior similar to that of FPS isolators under low excitations and transforms into a pure friction system under high excitations.The study proposes optimizing this VFPI,which features a polynomial function termed the Polynomial Friction Pendulum Isolator(PFPI),by introducing a suitable optimization function to minimize the acceleration transmitted to the superstructure,thereby improving the dynamic performance of the elevated storage tank.The research utilizes two wellestablished metaheuristic algorithms for optimization.It evaluates the effectiveness of the proposed isolator through time history analysis using the state space procedure under various ground motion records.Results,particularly under long-period ground motions,indicate a substantial reduction in the dynamic response of an elevated liquid storage tank equipped with the optimized PFPI.This underscores the potential of the proposed solution in enhancing the seismic resilience of liquid storage tanks.
文摘Turbulent flow over gravel beds in open channels is a fundamental yet complex problem in hydraulic engineering,as flow behavior is highly sensitive to channel geometry and bed roughness.In this study,the Volume of Fluid(VOF)method coupled with the standard k-εturbulence model is employed to simulate air-water interactions over gravel beds,with open boundary conditions capturing realistic channel-atmosphere interactions.Numerical simulations are performed to examine how channel design influences the relationship between the friction factor(f)and the Reynolds number(RN).Velocity and VOF contours indicate peak flow near the inlet,with a maximum velocity of 0.64 m/s.The simulations show strong agreement with theoretical predictions,yielding a correlation coefficient of 0.99 for RN,while f and Chezy’s coefficient(C)reach 0.75 and 0.71,respectively.Comparison with experimental measurements shows deviations of approximately 17% for RN,25% for f,and 12% for C.Moreover,further analysis confirms an inverse linear relationship between f and RN,in accordance with classical models such as Bazin’s curves,the Colebrook equation,and Moody’s approximation.Overall,the results demonstrate that the proposed numerical framework reliably captures flow dynamics over gravel beds,offering a robust tool for hydraulic design and performance assessment of open channels.
基金National Natural Science Foundation of China(grant number:52375224)Natural Science Foundation of Jiangsu Province(grant number:BK20242086)+2 种基金Priority Academic Program Development of Jiangsu Higher Education Institutions,a project supported by"the Fundamental Research Funds for the Central Universities"(grant number:202410976)Graduate Innovation Program of China University of Mining and Technology(grant number:2024WLKXJ075)Postgraduate Research&Practice Innovation Program of Jiangsu Province(grant number:KYCX24_2719).
文摘Pain,as a common symptom,seriously affects the patient's health.The aim of this work was to study the physiological responses of the brain and identify the features of Electroencephalography(EEG)signals related to friction pain.The results showed that the primary brain activation evoked by friction pain was located in the Prefrontal Cortex(PFC).The activation area decreased,and the negative activation intensity in the PFC region increased with increasing intensity of pain.The inhibitory interactions between different brain regions,especially between the PFC and primary somatosensory cortex(SI)regions were enhanced,and excitatory-inhibitory connections between the medial and lateral pain pathways were balanced during pain perception.The percentage power spectral density of theαrhythm(Dα),dominant singularity strength(αpeak)and longest vertical line(Vmax)of EEG signals induced by pain significantly decreased,and the percent-age power spectral density of theβrhythm(Dβ)significantly increased.The combination of multiple features of Dα,Dβ,αpeak and Vmax could significantly improve the average recognition accuracy of different pain states.This study elucidated the neural processing mechanisms of friction-induced pain,and EEG features associated with friction pain were extracted and recognized.It was helpful to study the brain feedback mechanisms of pain and control signals of Brain-Computer Interface(BCI)system related to pain.
基金the Postdoctoral Science Foundation Funded Project of China with grant No.2021M701687Introduction and Education Plan for Young Innovative Talents in Colleges and Universities of Shandong Province.
文摘UHMWPE(Ultra-High Molecular Weight Polyethylene)plain-weave fabric,characterized by its lightweight and high-strength properties,is widely used in protective equipment such as bulletproof vests and stab-resistant vests,serving as a key material for enhancing protective performance.This study systematically investigates the influence mechanism of interfacial properties on the energy absorption characteristics of UHMWPE-based protective structures through multi-scale experiments and numerical simulations,and establishes a cross-scale design methodology.Innovatively,an orthotropic constitutive model incorporating dynamic friction coefficients is constructed,combined with a modified Johnson-Cook failure criterion,to achieve high-precision simulation of the entire ballistic impact process(error<3.5%).Additionally,a friction field prediction model considering strain rate effects is developed,and the friction evolution laws of UHMWPE and Para-aramid(Kevlar)fabrics under strain rates of 10^(−3) and 10^(−4) s^(−1) are obtained through MTS pull-out tests.The results show that:(1)there exists a critical yarn-yarn friction coefficient(μ=0.2);exceeding this value leads to a 19%reduction in energy absorption capacity,while viscous interfaces increase the energy dissipation peak by 16%;(2)UHMWPE shows kinetically-dominated absorption(58%)with high rate but high load,increasing damage risk.Para-aramid has friction-dominated absorption(53%)with a lower rate but stable load.Hybrid fabrics use potential-dominated absorption(49%)at a moderate rate,balancing stability and protection.(3)3–5 layers of UHMWPE fabric yield optimal cost-effectiveness,with the unit cost reduction rate of the HS+5U scheme reaching 2.74 m/(s·$),which is 91%higher than that of the hybrid scheme.(4)For HS+5U(5-ply UHMWPE),V50 is 520 m/s,meeting primary protection requirement.For hybrid solutions with U/K≥3(e.g.,HS+6U+2K),V50 reaches 580 m/s(≥540 m/s),satisfying advanced protection requirement.This research provides critical references for the design of flexible protective structures and their engineering applications.
基金Wuxi University Research Start-up Fund for Introduced Talents(Grant No:2024r031)Technology Development Contract(Contract Registration Number:2024320205000963)+1 种基金National Natural Science Foundation of China(Grant No.52275288)Ningbo Key Research and Development Plan(Grant No.2023Z022).
文摘To solve the problem of abnormal abrasion of Cu-Based Friction Materials(CBFMs),Bionic Non-Smooth Surface(BNS)on friction surface of CBFMs was constructed based on bionic principles,and the optimal bionic prototype was selected by Finite Element Method(FEM).In addition,the bionic parameters were optimized by Response Surface Method(RSM).Samples holding BNS were prepared by Laser Processing,tribological properties were tested by a Friction and Wear Tester and worn surface morphology was characterized by a Scanning Electron Microscope(SEM).The results showed that BNS on friction surface could regulate the stress distribution and alleviate the peak stress.Among all samples,the coupled texture of pit-hexagonal got the minimum peak stress.During braking,bionic texture could also collect wear debris or change the motion forms from sliding to rotation,which can reduce abnormal abrasion.The wear rate was reduced by 19.31%.The results in this paper can provide a new idea for enhancing the tribological properties of CBFMs,and can also lay the foundation for further research of bionic tribology.
基金supported by the NSF of Shanxi(202303021221168)the Industry-university-research project of Shanxi Datong University(2022CXY10,2022CXY13).
文摘In this paper,our main goal is to study a new mathematical model which describes the frictional contact between a foundation and a deformable body which is composed of viscoplastic materials and where the process is considered dynamic.The contact condition on the normal plane is modeled by a unilateral constraint condition for a version of normal velocity in which the memory effect and the adhesion are considered.On the tangential plane a frictional contact condition is governed by the Clarke subdifferential of a locally Lipschitz function,and the evolution of the bonding field is governed by an ordinary differential equation.We formulate this problem as coupled system that consists of two ordinary differential equations and a variational-hemivariational inequality.Then,the existence,uniqueness and continuous dependence of the solution on the data results concerning the abstract system are established.Finally,we use the abstract results to show the existence and uniqueness of the solution to the contact problem.
基金National Natural Science Foundations of China(52275295)Central Plains Science and Technology Innovation Leading Talents(234200510026).
文摘Ion-exchange Polymer-Metal Composites(IPMCs)gain huge attentions due to large deformation,rapid electromechanical response,and high energy conversion efficiency.Deflection of IPMC arises from the volumetric swelling effect induced by the concentration gradient of hydrated cations between the two electrodes,thus the volume of hydrated cation deter-mines the motion magnitude and direction of IPMC.H ion is one of the most commonly used driving cations for IPMC.However,due to its unique characteristics,particularly the inability to accurately quantify its hydration volume,existing literatures primarily focus on the physical driving models for metallic cations,i.e.,Na+,no driving model for the H ion is reported until now.This paper proposes a novel model of H ion escape from the water's body-centered cubic lattice to count the hydration volume.Number(n)of water molecules carried by the H ion is solved by combining the Lennard-Jones potential energy function with Maxwell's velocity distribution.The specific n value is equivalent to 4.04 for the H ion inside Nafion electrolyte under a 3.0 V DC electric field.Substituting it into the classic Friction Model(proposed by Tadokoro et al.at 2000),actuation behaviors of H ion driven IPMC were therefore achieved through Matlab calculations and Abaqus simulations.The calculated results of dynamic displacement and force highly match to the experimental data form the Nafion IPMC actuator driven by same electric field,showing a highly reliability of the established escape model.
