Silicon,a leading candidate for electrode material for lithium-ion batteries,has garnered significant attention.During the initial lithiation process,the alloying reaction between silicon and lithium transforms the pr...Silicon,a leading candidate for electrode material for lithium-ion batteries,has garnered significant attention.During the initial lithiation process,the alloying reaction between silicon and lithium transforms the pristine silicon microstructure from crystalline to amorphous,resulting in plastic deformation of the amorphous phase.This study proposes the free volume theory to develop a fully coupled Cahn-Hilliard phase-field model that integrates viscoplastic deformation,free volume evolution,and diffusion.This model investigates the chemophysical phenomenon of self-limiting behavior occurring during the initial lithiation of silicon anodes.Unlike most existing models,the proposed model considers free volume-dependent diffusion using a physically-based approach.The model’s temporal variation in the lithiated phase thickness aligns well with experimental results,confirming the model’s accuracy.Stress field calculations reveal the coexistence of compressive and tensile stresses within the lithiated phase,which may not cause the limiting effect under the frame of the stress-induced diffusion.Analyses indicate that high effective stress increases free volume,enhancing lithium diffusion and augmenting the diffusion coefficient.Reducing the diffusion coefficient in the lithiated phase due to free volume evolution is the primary cause of self-limiting lithiation.展开更多
A new model for self-diffusion coefficients was proposed based oil both the concepts of molecular free volume and activation energy. The unknown parameters of this model were clearly defined and compared with the Chap...A new model for self-diffusion coefficients was proposed based oil both the concepts of molecular free volume and activation energy. The unknown parameters of this model were clearly defined and compared with the Chapman-Enskog model. At the same time a new method for calculating activation energy was devised and applied to the new model. In addition, the free volume was defined by implementing the generic van der Waals equation of state, the radial distribution function of which was obtained by using the Morsali- Goharshadi empirical formula. Under the same conditions, the new model was better than the original free volume model.展开更多
The effect of carbon black （CB） and graphite （G） powders on the macroscopic and nano-scale free volume properties of silicone rubber based on poly（di-methylsiloxane） （PDMS） was studied through thermal and cycl...The effect of carbon black （CB） and graphite （G） powders on the macroscopic and nano-scale free volume properties of silicone rubber based on poly（di-methylsiloxane） （PDMS） was studied through thermal and cyclic mechanical measurements, as well as with positron annihilation lifetime spectroscopy （PALS）. The melting temperature of the composites （Tm） and the endothermic enthalpy of melting （ΔHm） were estimated by differential scanning calorimetry （DSC）. Tm and the degree of crystallinity （χc） of PDMS composites were found to decrease with increasing the CB content. This can be explained due to the increase in physical cross-linking which results in a decrease in the crystallite thickness. Besides, χc was found to be dependent on the filler type. Cyclic stress-strain behavior of PDMS loaded with different contents of filler has been studied. Mullins ratio （RM） was found to be dependent on the filler type and content. It was found that, RM increases with increasing the filler content due to the increase in physical cross-linking which results in a decrease in the size of free volume, as observed through a decrease of the o-Ps lifetime τ3 measured by PALS. Moreover, the hysteresis in PDMS-CB composites was more pronounced than in PDMS-G composites. Furthermore, a correlation was established between the free volume Vf and the mechanical properties of PDMS composites containing different fillers. A negative correlation was observed between Vf and RM.展开更多
Positron annihilation lifetime spectroscopy （PALS） is a powerful technique for the study of free volume in polymers. The lifetime of ortho-positronium （o-Ps）, a bound state of an electron and a positron, can be us...Positron annihilation lifetime spectroscopy （PALS） is a powerful technique for the study of free volume in polymers. The lifetime of ortho-positronium （o-Ps）, a bound state of an electron and a positron, can be used to assess the pore size, while the intensity can be used to characterize the number of pores. Based on the values of the long-lived o-Ps components in the lifetime spectra, the radii and fractional free volumes of sulfonated poly （2,6-dimethyl-1,4- phenyleneoxide） （SPPO） membranes with added LiCl and SPPO-PES （Polyethersulfone） blend were compared. Free volume radii in both kinds of membranes are discussed.展开更多
The positron annihilation lifetime and ionic conductivity are each measured as a function of organophilic rectorite（OREC） content and temperature in a range from 160 K to 300 K.According to the variation of ortho-po...The positron annihilation lifetime and ionic conductivity are each measured as a function of organophilic rectorite（OREC） content and temperature in a range from 160 K to 300 K.According to the variation of ortho-positronium（o-Ps） lifetime with temperature,the glassy transition temperature is determined.The continuous maximum entropy lifetime（MELT） analysis clearly shows that the OREC and temperature have important effects on o-Ps lifetime and free volume distribution.The experimental results show that the temperature dependence of ionic conductivity obeys the Vogel-Tammann-Fulcher（VTF） and Williams-Landel-Ferry（WLF） equations,implying a free-volume transport mechanism.A linear least-squares procedure is used to evaluate the apparent activation energy related to the ionic transport in the VTF equation and several important parameters in the WLF equation.It is worthwhile to notice that a direct linear relationship between the ionic conductivity and free volume fraction is established using the WLF equation based on the free volume theory for nanocomposite electrolyte,which indicates that the segmental chain migration and ionic migration and diffusion could be explained by the free volume theory.展开更多
Positron annihilation lifetime (PAL) spectroscopy was applied to investigate the free volume properties of two types of simultaneous interpenetrating polymer networks (SINs), stoichiometric SINs and non--stoichiometri...Positron annihilation lifetime (PAL) spectroscopy was applied to investigate the free volume properties of two types of simultaneous interpenetrating polymer networks (SINs), stoichiometric SINs and non--stoichiometric SINs. PU/VER SINs are all composed of polyurethane(PU) and vinyl ester resin (VER)with different compositions. Mean free volume size in PU/VER deceased with the increase of VER weight percentage, and the relative intensity, relevant to free volume content, increased with VER contents. The effect of chemical bonds between PU networks and VER networks to free volume properties was observed. Results revealed that chemical bonds between the two networks led to molecular denser packing, free volume contraction and made stoichoimetric PU/VER SINs a miscible system.展开更多
Grain boundary plays a key role in electromigration process of polycrystal interconnection. We take a free volume to represent a ＇vacancy-ion complex＇ as a function of grain boundary specific resistivity, and develo...Grain boundary plays a key role in electromigration process of polycrystal interconnection. We take a free volume to represent a ＇vacancy-ion complex＇ as a function of grain boundary specific resistivity, and develop a new characterisation model for grain boundary noise. This model reveals the internal relation between the boundary scattering section and electromigration noise. Comparing the simulation result with our experimental result, we find the source as well as the form of noise change in the electromigration process. In order to describe the noise enhancement at grain boundary quantitatively, we propose a new parameter--grain boundary noise enhancement factor, which reflects that the grain boundary noise can characterise the electromigration damage sensitively.展开更多
A series of polyurethane/epoxy resin interpenetrating polymer networks （PU/ER IPN） were studied by positron annihilation lifetime spectroscopy （PALS）. The effects of epoxy resin type and content on the free volume...A series of polyurethane/epoxy resin interpenetrating polymer networks （PU/ER IPN） were studied by positron annihilation lifetime spectroscopy （PALS）. The effects of epoxy resin type and content on the free volume properties in IPN were investigated. We found that in PU/ER IPN, the free volume hole size and fractional free volume showed a negative deviation due to closer segmental chain packing through some chemical bonding between PU and epoxy resin. Direct relationship between the gas permeability and the free volume has been established based on the free volume theory. Experimental results revealed that the free volume plays an important role in determining the gas diffusion and permeability.展开更多
Free volume is an extremely important intrinsic defect in polymers. Structurally, free volume is the randomly distributed holes in the polymer molecular chain segments. In proton exchange membrane fuel cells, free vol...Free volume is an extremely important intrinsic defect in polymers. Structurally, free volume is the randomly distributed holes in the polymer molecular chain segments. In proton exchange membrane fuel cells, free volume is also the space needed for the directional conduction of protons. Irradiation by α particles to grafting sulfonated poly(vinylidene fluoride)(PVDF) is one of the methods to produce proton exchange membrane with good proton channel rate. Positron annihilation lifetime spectroscopy was used to study the free volume size at different absorbed dose levels from 0.13 MGy to 0.65 MGy. Measurement method of positron annihilation lifetime spectroscopy for PVDF based on ^(44) Ti positron source was developed. For low dose irradiation at 0.26 MGy, a decrease in free volume and practically unchanged crystallinity were observed. Further increase of absorbed dose range from 0.26 MGy to 0.39 MGy led to an increasing crystallinity with the same free volume level. For the absorbed dose from 0.39 MGy to 0.65 MGy, crystallinity was decreased but free volume remained almost constant.展开更多
The Double Take column looks at a single topic from an African and Chinese perspective.This month,we weigh the advantages of taking on debt against the benefits of staying debt-free.
The advancement of integrated die-casting technology calls for high-strength,high-ductility heat-treatment-free Al alloys.This study investigates the use of a new AlSiFeMnVTiSrZr heat-treatment-free die-casting alloy ...The advancement of integrated die-casting technology calls for high-strength,high-ductility heat-treatment-free Al alloys.This study investigates the use of a new AlSiFeMnVTiSrZr heat-treatment-free die-casting alloy for shock tower manufacturing.Results show the alloy has excellent overall mechanical properties,but significant regional differences in microstructure and performance are found in the shock tower casting:Far-gate Position 6 has almost no externally solidified crystals(ESCs),whereas dense coarse dendritic ESCs exist in the center of near-gate Position 5.The fracture surface of Position 6 shows a steeper slope,while Position 5 has a rough crack propagation platform.Far-gate Position 6 also has higher porosity(nearly triple that of near-gate Region 5)and larger average pore size.Analysis reveals microstructural heterogeneity between near-and far-gate regions strongly influences mechanical performance.Notably,coarse dendritic ESCs in the near-gate region restrict grain boundary strengthening,leading to lower yield strength despite low porosity.Conversely,while fine grains in the far-gate region could enhance grain boundary strengthening,abundant porosity acts as crack initiation sites,severely reducing ductility.These findings provide theoretical guidance for evaluating integrated die-cast component performance.展开更多
This study investigates the uncertain dynamic characterization of hybrid composite plates by employing advanced machine-assisted finite element methodologies.Hybrid composites,widely used in aerospace,automotive,and s...This study investigates the uncertain dynamic characterization of hybrid composite plates by employing advanced machine-assisted finite element methodologies.Hybrid composites,widely used in aerospace,automotive,and structural applications,often face variability in material properties,geometric configurations,and manufacturing processes,leading to uncertainty in their dynamic response.To address this,three surrogate-based machine learning approaches like radial basis function(RBF),multivariate adaptive regression splines(MARS),and polynomial neural networks(PNN)are integrated with a finite element framework to efficiently capture the stochastic behavior of these plates.The research focuses on predicting the first three natural frequencies under material uncertainties,which are critical to ensuring structural reliability.Monte Carlo simulation(MCS)is used as a benchmark for generating probabilistic datasets,including mean values,standard deviations,and probability density functions.The surrogate models are then trained and validated against these datasets,enabling accurate representation of uncertainty with substantially fewer samples compared to conventionalMCS.Among the methods studied,the RBFmodel demonstrates superior performance,closely approximating MCS results with a reduced sample size,thereby achieving significant computational savings.The proposed framework not only reduces computational time and costs but also maintains high predictive accuracy,making it well-suited for complex engineering systems.Beyond free vibration analysis,the methodology can be extended to more sophisticated scenarios,such as forced vibration,damping effects,and nonlinear structural responses.Overall,this work presents a computationally efficient and robust approach for surrogate-based uncertainty quantification,advancing the analysis and design of hybrid composite structures under uncertainty.展开更多
Alkali-free SiO_(2)-Al_(2)O_(3)-CaO-MgO with different SiO_(2)/Al_(2)O_(3)mass ratios was prepared by conventional melt quenching method.The glass network structure,thermodynamic properties and elastic modulus changes...Alkali-free SiO_(2)-Al_(2)O_(3)-CaO-MgO with different SiO_(2)/Al_(2)O_(3)mass ratios was prepared by conventional melt quenching method.The glass network structure,thermodynamic properties and elastic modulus changes with SiO_(2)and Al_(2)O_(3)ratios were investigated using various techniques.It is found that when SiO_(2)is replaced by Al_(2)O_(3),the Q^(4) to Q^(3) transition of silicon-oxygen network decreases while the aluminum-oxygen network increases,which result in the transformation of Si-O-Si bonds to Si-O-Al bonds and an increase in glass network connectivity even though the intermolecular bond strength decreases.The glass transition temperature(T_(g))increases continuously,while the thermal expansion coefficient increases and high-temperature viscosity first decreases and then increases.Meanwhile,the elastic modulus values increase from 93 to 102 GPa.This indicates that the elastic modulus is mainly affected by packing factor and dissociation energy,and elements with higher packing factors and dissociation energies supplant those with lower values,resulting in increased rigidity within the glass.展开更多
As a controllable power generation method requiring no energy storage,Ocean Thermal Energy Conversion(OTEC)technology demonstrates characteristics of abundant reserves,low pollution,and round-the-clock stable operatio...As a controllable power generation method requiring no energy storage,Ocean Thermal Energy Conversion(OTEC)technology demonstrates characteristics of abundant reserves,low pollution,and round-the-clock stable operation.The free-standing cold-water pipe(CWP)in the system withstands various complex loads during operation,posing potential failure risks.To reveal the deformation and stress mechanisms of OTEC CWPs,this study first analyzes wave particle velocity and acceleration to determine wave loads at different water depths.Based on the Euler-Bernoulli beam model,a quasi-static load calculation model for OTEC CWPs was established.The governing equations were discretized using the finite difference method,and matrix equations were solved to analyze bending deformation,bending moments,and surface stresses at discrete points along the pipe.Results indicate that water depths within 50 m represent a critical zone where wave particle velocity,acceleration,and wave loads exhibit significant variations in harmonic patterns,while beyond 50 m depth wave loads decrease linearly.Ocean currents and surface wind-driven currents substantially influence the CWP’s lateral displacement.Considering the effect of clump weights,the maximum lateral displacement occurs at 600–800 m below sea level.Utilizing large-wall-thickness high-strength pipes at the top section significantly enhances the structural safety of the CWP system.展开更多
Objective: To investigate whether attaching a free lens anterior capsular disc to the corneal endothelial surface during femtosecond laser-assisted cataract surgery (FLACS) can effectively reduce postoperative corneal...Objective: To investigate whether attaching a free lens anterior capsular disc to the corneal endothelial surface during femtosecond laser-assisted cataract surgery (FLACS) can effectively reduce postoperative corneal endothelial cell loss. Methods: This prospective study included 97 cataract patients. Among them, 33 patients served as the experimental group, where a free lens anterior capsular disc was applied for corneal endothelial protection during FLACS. The remaining 64 patients formed the control group and underwent conventional FLACS. Changes in corneal endothelial cell density were compared between the two groups before surgery and one month postoperatively. Results: One month after surgery, corneal endothelial cell counts in both groups were lower than preoperative levels. However, the experimental group exhibited higher corneal endothelial cell counts than the control group, with a smaller reduction in cell counts (p < 0.05). The corneal endothelial cell loss rate in the experimental group was lower than that in the control group one month postoperatively (p < 0.05). At the one-month follow-up, there were no significant differences in LogMAR visual acuity or non-contact intraocular pressure between the two groups compared to preoperative values (p > 0.05). Additionally, no significant differences were observed between the experimental and control groups in terms of LogMAR visual acuity, non-contact intraocular pressure, improvements in LogMAR visual acuity, or changes in non-contact intraocular pressure (p > 0.05). Conclusion: Attaching a free lens anterior capsular disc to the corneal endothelial surface during FLACS can effectively reduce intraoperative corneal endothelial cell loss.展开更多
The remarkable mechanical and physical characteristics of functionally graded(FG)graphene origami(GOri)-enabled auxetic metamaterial(GOEAM)structures,including their high strength-to-weight ratio,tunable stiffness and...The remarkable mechanical and physical characteristics of functionally graded(FG)graphene origami(GOri)-enabled auxetic metamaterial(GOEAM)structures,including their high strength-to-weight ratio,tunable stiffness and strength,and negative Poisson's ratio(NPR),have demonstrated significant promise for a range of engineering applications.This paper aims to investigate the nonlinear free vibrations behaviors of FG-GOEAM non-uniform thickness skew-microplate with rectangular and elliptical planform and resting on Kerr-elastic foundation in thermal environment.Within the framework of the higher-order shear deformation theory(HSDT),von Kármán assumption,modified couple stress theory(MCST)and by employing Hamilton's principle the nonlinear governing equations of motion are established.By combining an iterative technique with a displacement control strategy,an isogeometric analysis(IGA)approach used to determine the nonlinearity in free vibration,as measured by the nonlinear frequency ratio associated with the center deflection amplitude.The effects of GOri distribution patterns,weight fraction,length-scale parameter,temperature difference,skew-angle,and micro-plate dimensions on the nonlinear free vibrations behaviors of the FG-GOEAM non-uniform thickness skew-microplate are revealed through a thorough parametric study.This result can be applied in studies on the design of micro-electro-mechanical devices operating in various complex environments and conditions.展开更多
Halogens are common in industrial thermal processes and can induce formation of toxic organic pollutants.Currently,the specific effects of coexisting halogens on toxic pollutant formation are unclear.In this study,we ...Halogens are common in industrial thermal processes and can induce formation of toxic organic pollutants.Currently,the specific effects of coexisting halogens on toxic pollutant formation are unclear.In this study,we found the boosting effects of halogens on organic pollutants formation during thermal processes.In situ electron paramagnetic resonance spectroscopy was used to distinguish the organic free radical intermediates of organic pollutants during thermal processes.The pure chlorine-containing reaction system dominantly induce the formation of highly chlorinated phenoxy radicals,whereas the pure bromine-containing reaction system induce the formation of semiquinone radicals.The results provide clear evidence for the molecular mechanisms by which halogen coexistence boosts pollutants formation.Coexisting halogens made the reactions much more complex.Bromine atom radicals(Br·)can enhance the level of active chlorine atoms radicals(Cl·),then(1)facilitating highly chlorinated organic radicals and toxic pollutants formation,(2)activating polycyclic aromatic hydrocarbons molecules for subsequent ring growth and(3)accelerating oxidation reactions.Combining the identification of organic free radical intermediates and characteristics of products,detailed mechanisms of halogens on the formations of organic pollutants during thermal-related processes were clarified,which can be helpful for their efficient control in the widespread bromines and chlorines co-existence reaction system.展开更多
Since the launch of island-wide special customs operations at Hainan Free Trade Port(Hainan FTP),the proportion of “zero-tariff”imported goods has increased significantly from 21 to 74 percent, and high-quality good...Since the launch of island-wide special customs operations at Hainan Free Trade Port(Hainan FTP),the proportion of “zero-tariff”imported goods has increased significantly from 21 to 74 percent, and high-quality goods from Southeast Asia can enter Hainan at a more competitive price. If goods contain imported materials and achieve at least 30 percent added value through local processing,they can enter the Chinese mainland market with an exemption from import tariffs, effectively gaining market access across China.展开更多
The world economy is now in a period of indepth adjustment.The intensification of geopolitical conflicts,a rise of trade protectionism,and reconfiguration of global supply chains have prompted all countries to re-exam...The world economy is now in a period of indepth adjustment.The intensification of geopolitical conflicts,a rise of trade protectionism,and reconfiguration of global supply chains have prompted all countries to re-examine their openness to trade amid rising uncertainties.Against this backdrop,China’s continuing commitment to promoting higherlevel opening up and building the Hainan Free Trade Port(Hainan FTP)has distinct contemporary significance and strategic value.展开更多
The dedicated freight channel at the Youyiguan Border Gate in south China’s Guangxi Zhuang Autonomous Region buzzes with activity as trucks loaded with export goods move steadily through customs.Thanks to a system up...The dedicated freight channel at the Youyiguan Border Gate in south China’s Guangxi Zhuang Autonomous Region buzzes with activity as trucks loaded with export goods move steadily through customs.Thanks to a system upgraded at the start of 2026,clearance personnel at this China-Vietnam crossing simply place an order online,and the entire process is handled almost instantly via an intelligent platform.Adding to the efficiency,the border gate also features dedicated lanes that support driverless container trucks.展开更多
基金the National Natural Science Foundation of China under grant No.12372173the Natural Science Foundation of Shanghai under grant No.23ZR1468600.
文摘Silicon,a leading candidate for electrode material for lithium-ion batteries,has garnered significant attention.During the initial lithiation process,the alloying reaction between silicon and lithium transforms the pristine silicon microstructure from crystalline to amorphous,resulting in plastic deformation of the amorphous phase.This study proposes the free volume theory to develop a fully coupled Cahn-Hilliard phase-field model that integrates viscoplastic deformation,free volume evolution,and diffusion.This model investigates the chemophysical phenomenon of self-limiting behavior occurring during the initial lithiation of silicon anodes.Unlike most existing models,the proposed model considers free volume-dependent diffusion using a physically-based approach.The model’s temporal variation in the lithiated phase thickness aligns well with experimental results,confirming the model’s accuracy.Stress field calculations reveal the coexistence of compressive and tensile stresses within the lithiated phase,which may not cause the limiting effect under the frame of the stress-induced diffusion.Analyses indicate that high effective stress increases free volume,enhancing lithium diffusion and augmenting the diffusion coefficient.Reducing the diffusion coefficient in the lithiated phase due to free volume evolution is the primary cause of self-limiting lithiation.
文摘A new model for self-diffusion coefficients was proposed based oil both the concepts of molecular free volume and activation energy. The unknown parameters of this model were clearly defined and compared with the Chapman-Enskog model. At the same time a new method for calculating activation energy was devised and applied to the new model. In addition, the free volume was defined by implementing the generic van der Waals equation of state, the radial distribution function of which was obtained by using the Morsali- Goharshadi empirical formula. Under the same conditions, the new model was better than the original free volume model.
文摘The effect of carbon black （CB） and graphite （G） powders on the macroscopic and nano-scale free volume properties of silicone rubber based on poly（di-methylsiloxane） （PDMS） was studied through thermal and cyclic mechanical measurements, as well as with positron annihilation lifetime spectroscopy （PALS）. The melting temperature of the composites （Tm） and the endothermic enthalpy of melting （ΔHm） were estimated by differential scanning calorimetry （DSC）. Tm and the degree of crystallinity （χc） of PDMS composites were found to decrease with increasing the CB content. This can be explained due to the increase in physical cross-linking which results in a decrease in the crystallite thickness. Besides, χc was found to be dependent on the filler type. Cyclic stress-strain behavior of PDMS loaded with different contents of filler has been studied. Mullins ratio （RM） was found to be dependent on the filler type and content. It was found that, RM increases with increasing the filler content due to the increase in physical cross-linking which results in a decrease in the size of free volume, as observed through a decrease of the o-Ps lifetime τ3 measured by PALS. Moreover, the hysteresis in PDMS-CB composites was more pronounced than in PDMS-G composites. Furthermore, a correlation was established between the free volume Vf and the mechanical properties of PDMS composites containing different fillers. A negative correlation was observed between Vf and RM.
基金supported by National Natural Science Foundation (No. 60602065)Innovation Funds of University of Science and Technology of China for Graduate Student (No.KD2006009)
文摘Positron annihilation lifetime spectroscopy （PALS） is a powerful technique for the study of free volume in polymers. The lifetime of ortho-positronium （o-Ps）, a bound state of an electron and a positron, can be used to assess the pore size, while the intensity can be used to characterize the number of pores. Based on the values of the long-lived o-Ps components in the lifetime spectra, the radii and fractional free volumes of sulfonated poly （2,6-dimethyl-1,4- phenyleneoxide） （SPPO） membranes with added LiCl and SPPO-PES （Polyethersulfone） blend were compared. Free volume radii in both kinds of membranes are discussed.
基金Project supported by the National Natural Science Foundation of China (Grant No. 11175134)
文摘The positron annihilation lifetime and ionic conductivity are each measured as a function of organophilic rectorite（OREC） content and temperature in a range from 160 K to 300 K.According to the variation of ortho-positronium（o-Ps） lifetime with temperature,the glassy transition temperature is determined.The continuous maximum entropy lifetime（MELT） analysis clearly shows that the OREC and temperature have important effects on o-Ps lifetime and free volume distribution.The experimental results show that the temperature dependence of ionic conductivity obeys the Vogel-Tammann-Fulcher（VTF） and Williams-Landel-Ferry（WLF） equations,implying a free-volume transport mechanism.A linear least-squares procedure is used to evaluate the apparent activation energy related to the ionic transport in the VTF equation and several important parameters in the WLF equation.It is worthwhile to notice that a direct linear relationship between the ionic conductivity and free volume fraction is established using the WLF equation based on the free volume theory for nanocomposite electrolyte,which indicates that the segmental chain migration and ionic migration and diffusion could be explained by the free volume theory.
文摘Positron annihilation lifetime (PAL) spectroscopy was applied to investigate the free volume properties of two types of simultaneous interpenetrating polymer networks (SINs), stoichiometric SINs and non--stoichiometric SINs. PU/VER SINs are all composed of polyurethane(PU) and vinyl ester resin (VER)with different compositions. Mean free volume size in PU/VER deceased with the increase of VER weight percentage, and the relative intensity, relevant to free volume content, increased with VER contents. The effect of chemical bonds between PU networks and VER networks to free volume properties was observed. Results revealed that chemical bonds between the two networks led to molecular denser packing, free volume contraction and made stoichoimetric PU/VER SINs a miscible system.
基金supported by the National Natural Science Foundation of China (Grant No.60376023)the Innovative Foundation of Xi’an Applied Materials Inc.China (Grant No.XA-AM-200603)
文摘Grain boundary plays a key role in electromigration process of polycrystal interconnection. We take a free volume to represent a ＇vacancy-ion complex＇ as a function of grain boundary specific resistivity, and develop a new characterisation model for grain boundary noise. This model reveals the internal relation between the boundary scattering section and electromigration noise. Comparing the simulation result with our experimental result, we find the source as well as the form of noise change in the electromigration process. In order to describe the noise enhancement at grain boundary quantitatively, we propose a new parameter--grain boundary noise enhancement factor, which reflects that the grain boundary noise can characterise the electromigration damage sensitively.
基金Supported by the National Natural Science Foundation of China (20374038)
文摘A series of polyurethane/epoxy resin interpenetrating polymer networks （PU/ER IPN） were studied by positron annihilation lifetime spectroscopy （PALS）. The effects of epoxy resin type and content on the free volume properties in IPN were investigated. We found that in PU/ER IPN, the free volume hole size and fractional free volume showed a negative deviation due to closer segmental chain packing through some chemical bonding between PU and epoxy resin. Direct relationship between the gas permeability and the free volume has been established based on the free volume theory. Experimental results revealed that the free volume plays an important role in determining the gas diffusion and permeability.
文摘Free volume is an extremely important intrinsic defect in polymers. Structurally, free volume is the randomly distributed holes in the polymer molecular chain segments. In proton exchange membrane fuel cells, free volume is also the space needed for the directional conduction of protons. Irradiation by α particles to grafting sulfonated poly(vinylidene fluoride)(PVDF) is one of the methods to produce proton exchange membrane with good proton channel rate. Positron annihilation lifetime spectroscopy was used to study the free volume size at different absorbed dose levels from 0.13 MGy to 0.65 MGy. Measurement method of positron annihilation lifetime spectroscopy for PVDF based on ^(44) Ti positron source was developed. For low dose irradiation at 0.26 MGy, a decrease in free volume and practically unchanged crystallinity were observed. Further increase of absorbed dose range from 0.26 MGy to 0.39 MGy led to an increasing crystallinity with the same free volume level. For the absorbed dose from 0.39 MGy to 0.65 MGy, crystallinity was decreased but free volume remained almost constant.
文摘The Double Take column looks at a single topic from an African and Chinese perspective.This month,we weigh the advantages of taking on debt against the benefits of staying debt-free.
基金the National Natural Science Foundation of China(Grant Nos.52405342 and 52175335)the National Key Research and Development Program of China(Grant No.2022YFB3404201)+2 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.N2302014 and N25ZJL003)the Natural Science Foundation Joint Foundation of Liaoning province(Grant No.2023-BSBA-108)the help provided by China FAW Foundry Co.,Ltd.
文摘The advancement of integrated die-casting technology calls for high-strength,high-ductility heat-treatment-free Al alloys.This study investigates the use of a new AlSiFeMnVTiSrZr heat-treatment-free die-casting alloy for shock tower manufacturing.Results show the alloy has excellent overall mechanical properties,but significant regional differences in microstructure and performance are found in the shock tower casting:Far-gate Position 6 has almost no externally solidified crystals(ESCs),whereas dense coarse dendritic ESCs exist in the center of near-gate Position 5.The fracture surface of Position 6 shows a steeper slope,while Position 5 has a rough crack propagation platform.Far-gate Position 6 also has higher porosity(nearly triple that of near-gate Region 5)and larger average pore size.Analysis reveals microstructural heterogeneity between near-and far-gate regions strongly influences mechanical performance.Notably,coarse dendritic ESCs in the near-gate region restrict grain boundary strengthening,leading to lower yield strength despite low porosity.Conversely,while fine grains in the far-gate region could enhance grain boundary strengthening,abundant porosity acts as crack initiation sites,severely reducing ductility.These findings provide theoretical guidance for evaluating integrated die-cast component performance.
文摘This study investigates the uncertain dynamic characterization of hybrid composite plates by employing advanced machine-assisted finite element methodologies.Hybrid composites,widely used in aerospace,automotive,and structural applications,often face variability in material properties,geometric configurations,and manufacturing processes,leading to uncertainty in their dynamic response.To address this,three surrogate-based machine learning approaches like radial basis function(RBF),multivariate adaptive regression splines(MARS),and polynomial neural networks(PNN)are integrated with a finite element framework to efficiently capture the stochastic behavior of these plates.The research focuses on predicting the first three natural frequencies under material uncertainties,which are critical to ensuring structural reliability.Monte Carlo simulation(MCS)is used as a benchmark for generating probabilistic datasets,including mean values,standard deviations,and probability density functions.The surrogate models are then trained and validated against these datasets,enabling accurate representation of uncertainty with substantially fewer samples compared to conventionalMCS.Among the methods studied,the RBFmodel demonstrates superior performance,closely approximating MCS results with a reduced sample size,thereby achieving significant computational savings.The proposed framework not only reduces computational time and costs but also maintains high predictive accuracy,making it well-suited for complex engineering systems.Beyond free vibration analysis,the methodology can be extended to more sophisticated scenarios,such as forced vibration,damping effects,and nonlinear structural responses.Overall,this work presents a computationally efficient and robust approach for surrogate-based uncertainty quantification,advancing the analysis and design of hybrid composite structures under uncertainty.
基金Supported by the National Key Research Program(No.2024-1129-954-112)National Natural Science Foundation of China(No.52372033)Guangxi Science and Technology Major Program(No.AA24263054)。
文摘Alkali-free SiO_(2)-Al_(2)O_(3)-CaO-MgO with different SiO_(2)/Al_(2)O_(3)mass ratios was prepared by conventional melt quenching method.The glass network structure,thermodynamic properties and elastic modulus changes with SiO_(2)and Al_(2)O_(3)ratios were investigated using various techniques.It is found that when SiO_(2)is replaced by Al_(2)O_(3),the Q^(4) to Q^(3) transition of silicon-oxygen network decreases while the aluminum-oxygen network increases,which result in the transformation of Si-O-Si bonds to Si-O-Al bonds and an increase in glass network connectivity even though the intermolecular bond strength decreases.The glass transition temperature(T_(g))increases continuously,while the thermal expansion coefficient increases and high-temperature viscosity first decreases and then increases.Meanwhile,the elastic modulus values increase from 93 to 102 GPa.This indicates that the elastic modulus is mainly affected by packing factor and dissociation energy,and elements with higher packing factors and dissociation energies supplant those with lower values,resulting in increased rigidity within the glass.
基金funded by Nansha District Science and Technology Project(Grant Number.2024ZD008)funded by China Geological Survey(Grant number:No.DD20230066,DD20242659).
文摘As a controllable power generation method requiring no energy storage,Ocean Thermal Energy Conversion(OTEC)technology demonstrates characteristics of abundant reserves,low pollution,and round-the-clock stable operation.The free-standing cold-water pipe(CWP)in the system withstands various complex loads during operation,posing potential failure risks.To reveal the deformation and stress mechanisms of OTEC CWPs,this study first analyzes wave particle velocity and acceleration to determine wave loads at different water depths.Based on the Euler-Bernoulli beam model,a quasi-static load calculation model for OTEC CWPs was established.The governing equations were discretized using the finite difference method,and matrix equations were solved to analyze bending deformation,bending moments,and surface stresses at discrete points along the pipe.Results indicate that water depths within 50 m represent a critical zone where wave particle velocity,acceleration,and wave loads exhibit significant variations in harmonic patterns,while beyond 50 m depth wave loads decrease linearly.Ocean currents and surface wind-driven currents substantially influence the CWP’s lateral displacement.Considering the effect of clump weights,the maximum lateral displacement occurs at 600–800 m below sea level.Utilizing large-wall-thickness high-strength pipes at the top section significantly enhances the structural safety of the CWP system.
基金Task Contract for the 2022 Dongguan Social Development Science and Technology Project,Project Name:Clinical Study on the Protection of Corneal Endothelium by the Anterior Capsular Flap in LenSx Femtosecond Laser-Assisted Cataract Surgery(Project No.:20221800901212)。
文摘Objective: To investigate whether attaching a free lens anterior capsular disc to the corneal endothelial surface during femtosecond laser-assisted cataract surgery (FLACS) can effectively reduce postoperative corneal endothelial cell loss. Methods: This prospective study included 97 cataract patients. Among them, 33 patients served as the experimental group, where a free lens anterior capsular disc was applied for corneal endothelial protection during FLACS. The remaining 64 patients formed the control group and underwent conventional FLACS. Changes in corneal endothelial cell density were compared between the two groups before surgery and one month postoperatively. Results: One month after surgery, corneal endothelial cell counts in both groups were lower than preoperative levels. However, the experimental group exhibited higher corneal endothelial cell counts than the control group, with a smaller reduction in cell counts (p < 0.05). The corneal endothelial cell loss rate in the experimental group was lower than that in the control group one month postoperatively (p < 0.05). At the one-month follow-up, there were no significant differences in LogMAR visual acuity or non-contact intraocular pressure between the two groups compared to preoperative values (p > 0.05). Additionally, no significant differences were observed between the experimental and control groups in terms of LogMAR visual acuity, non-contact intraocular pressure, improvements in LogMAR visual acuity, or changes in non-contact intraocular pressure (p > 0.05). Conclusion: Attaching a free lens anterior capsular disc to the corneal endothelial surface during FLACS can effectively reduce intraoperative corneal endothelial cell loss.
文摘The remarkable mechanical and physical characteristics of functionally graded(FG)graphene origami(GOri)-enabled auxetic metamaterial(GOEAM)structures,including their high strength-to-weight ratio,tunable stiffness and strength,and negative Poisson's ratio(NPR),have demonstrated significant promise for a range of engineering applications.This paper aims to investigate the nonlinear free vibrations behaviors of FG-GOEAM non-uniform thickness skew-microplate with rectangular and elliptical planform and resting on Kerr-elastic foundation in thermal environment.Within the framework of the higher-order shear deformation theory(HSDT),von Kármán assumption,modified couple stress theory(MCST)and by employing Hamilton's principle the nonlinear governing equations of motion are established.By combining an iterative technique with a displacement control strategy,an isogeometric analysis(IGA)approach used to determine the nonlinearity in free vibration,as measured by the nonlinear frequency ratio associated with the center deflection amplitude.The effects of GOri distribution patterns,weight fraction,length-scale parameter,temperature difference,skew-angle,and micro-plate dimensions on the nonlinear free vibrations behaviors of the FG-GOEAM non-uniform thickness skew-microplate are revealed through a thorough parametric study.This result can be applied in studies on the design of micro-electro-mechanical devices operating in various complex environments and conditions.
基金supported by the National Key Research and Development Program of China(No.2023YFC3707004)the National Natural Science Foundation of China(Nos.22376204,22076201 and 92143201)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Nos.XDB0750400,XDB0750100 and XDB0750000)the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(No.2019 QZKK0605).
文摘Halogens are common in industrial thermal processes and can induce formation of toxic organic pollutants.Currently,the specific effects of coexisting halogens on toxic pollutant formation are unclear.In this study,we found the boosting effects of halogens on organic pollutants formation during thermal processes.In situ electron paramagnetic resonance spectroscopy was used to distinguish the organic free radical intermediates of organic pollutants during thermal processes.The pure chlorine-containing reaction system dominantly induce the formation of highly chlorinated phenoxy radicals,whereas the pure bromine-containing reaction system induce the formation of semiquinone radicals.The results provide clear evidence for the molecular mechanisms by which halogen coexistence boosts pollutants formation.Coexisting halogens made the reactions much more complex.Bromine atom radicals(Br·)can enhance the level of active chlorine atoms radicals(Cl·),then(1)facilitating highly chlorinated organic radicals and toxic pollutants formation,(2)activating polycyclic aromatic hydrocarbons molecules for subsequent ring growth and(3)accelerating oxidation reactions.Combining the identification of organic free radical intermediates and characteristics of products,detailed mechanisms of halogens on the formations of organic pollutants during thermal-related processes were clarified,which can be helpful for their efficient control in the widespread bromines and chlorines co-existence reaction system.
文摘Since the launch of island-wide special customs operations at Hainan Free Trade Port(Hainan FTP),the proportion of “zero-tariff”imported goods has increased significantly from 21 to 74 percent, and high-quality goods from Southeast Asia can enter Hainan at a more competitive price. If goods contain imported materials and achieve at least 30 percent added value through local processing,they can enter the Chinese mainland market with an exemption from import tariffs, effectively gaining market access across China.
文摘The world economy is now in a period of indepth adjustment.The intensification of geopolitical conflicts,a rise of trade protectionism,and reconfiguration of global supply chains have prompted all countries to re-examine their openness to trade amid rising uncertainties.Against this backdrop,China’s continuing commitment to promoting higherlevel opening up and building the Hainan Free Trade Port(Hainan FTP)has distinct contemporary significance and strategic value.
文摘The dedicated freight channel at the Youyiguan Border Gate in south China’s Guangxi Zhuang Autonomous Region buzzes with activity as trucks loaded with export goods move steadily through customs.Thanks to a system upgraded at the start of 2026,clearance personnel at this China-Vietnam crossing simply place an order online,and the entire process is handled almost instantly via an intelligent platform.Adding to the efficiency,the border gate also features dedicated lanes that support driverless container trucks.
