Structural parameters of 22 polyacrylic compounds were computed at two levels using Hartree-Fock and DFT methods. Based on the experimental data of glass transition temperature （Tg）, four-parameter （energy of the l...Structural parameters of 22 polyacrylic compounds were computed at two levels using Hartree-Fock and DFT methods. Based on the experimental data of glass transition temperature （Tg）, four-parameter （energy of the lowest unoccupied molecular orbital （ELoMO）, the highest positive charge （Qmax^＋）, dipole moments（μ） and the next highest occupied molecular orbital （ENLOMO）） dependent equations were developed using structural parameters as theoretical descriptors. Especially, Tg dependent equation calculated at the HF/6-31G（d） level is more advantageous than others in view of their correlation and predictive abilities. This dependent equation was validated by variance inflation factors （VIF） and t-test methods.展开更多
The VO2 powders were prepared by hydrothermal synthesis.The effects of heat treatment conditions and Y-doping on the structure and phase transition temperature of VO2 were studied.The XRD,SEM and TEM results show that...The VO2 powders were prepared by hydrothermal synthesis.The effects of heat treatment conditions and Y-doping on the structure and phase transition temperature of VO2 were studied.The XRD,SEM and TEM results show that the heat treatment temperature has a significant effect on the crystal transformation of VO2 precursor.Increasing temperature is conducive to the transformation of precursor VO2(B)to ultrafine VO2(M).The Y-doping affects the structure of VO2.Y^3+can occupy the lattice position of V4+to form YVO4 solid solution,which can increase the cell parameters of VO2.Due to the lattice deformation caused by Y-doping,the aggregation of particles is prevented,and the grain is refined obviously.DSC curves show that Y-doping can reduce the phase transition temperature of VO2(M).After adding 9 at.%Y,the phase transition temperature can be reduced from 68.3 to 61.3℃.展开更多
The superconductivity of iron-based superconductor SmO 0.7 F 0.2 FeAs was investigated. The SmO 0.7 F 0.2 FeAs sample was prepared by the two-step solid-state reaction method. The onset resistivity transition temperat...The superconductivity of iron-based superconductor SmO 0.7 F 0.2 FeAs was investigated. The SmO 0.7 F 0.2 FeAs sample was prepared by the two-step solid-state reaction method. The onset resistivity transition temperature is as high as 56.5 K. X-ray diffraction （XRD） results show that the lattice parameters a and c are 0.39261 and 0.84751 nm, respectively. Furthermore, the global J c was more than 2.3 × 10 5 A/cm 2 at T = 10 K and H = 9 T, which was calculated by the formula of J c = 20ΔM/[a（1-a/（3b））]. The upper critical fields, H c2 ≈ 256 T （T = 0 K）, was determined according to the Werthamer-Helfand-Hohenberg formula, indicating that the SmO 0.7 F 0.2 FeAs was a superconductor with a very promising application.展开更多
On the basis of analysis of low carbon steel fracture macro-features and micro-processes at low temperature,the definition was given of the characteristic transition temperature of brittleness,T_(pm),and its physical ...On the basis of analysis of low carbon steel fracture macro-features and micro-processes at low temperature,the definition was given of the characteristic transition temperature of brittleness,T_(pm),and its physical meaning was expounded.Discussion was carried out of phys- ical characteristic of variation at T_(pm) in respect of the fracture toughness and property of crack arrest.In addition,research was made on the application of T_(pm),which can give infor- mation about the transition of the fracture toughness,the property of crack arrest and critical crack size,to estimation the brittleness of low carbon steel at low temperatures.展开更多
The effect of Al content on the ductile-brittle transition temperature of Al-Si coating and the effect of fracture behaviour.of the Al-Si coating on the fatigue properties of Ni-base superallovs have been investigated...The effect of Al content on the ductile-brittle transition temperature of Al-Si coating and the effect of fracture behaviour.of the Al-Si coating on the fatigue properties of Ni-base superallovs have been investigated to propose the theoretical basis of search for an optimum of mechanical properties of the high temperature coating on Ni-base alloys.展开更多
High pressure is an effective method to induce structural and electronic changes,creating novel high-pressure structures with excellent physical and chemical properties.Herein,we investigate the structural phase trans...High pressure is an effective method to induce structural and electronic changes,creating novel high-pressure structures with excellent physical and chemical properties.Herein,we investigate the structural phase transition of hafnium dihydrogen(HfH2)in a pressure range of 0 GPa-500 GPa through the first-principles calculations and the crystal structure analysis by particle swarm optimization(CALYPSO)code.The high-pressure phase transition sequence of HfH2is I4/mmm→Cmma→P-3m1 and the two phase transition pressure points are 220.21 GPa and 359.18 GPa,respectively.A newly trigonal P-3m1 structure with 10-fold coordination first appears as an energy superior structure under high pressure.These three structures are all metallic with the internal ionic bonding of Hf and H atoms.Moreover,the superconducting transition temperature(Tc)values of Cmma at 300 GPa and P-3m1 at 500 GPa are 3.439 K and 19.737 K,respectively.Interestingly,the superconducting transition temperature of the P-3m1 structure presents an upward trend with the pressure rising,which can be attributed to the increase of electron-phonon coupling caused by the enhanced Hf-d electronic density of states at Fermi level under high pressure.展开更多
In this study, it was examined whether the dynamics of polymer chains at a surface is different from that in thebulk, and if so, to what extent they differ in terms of surface glass transition temperature and diffusio...In this study, it was examined whether the dynamics of polymer chains at a surface is different from that in thebulk, and if so, to what extent they differ in terms of surface glass transition temperature and diffusion coefficient. Obtainedresults clearly indicate that surface chains can travel for a relatively large distance in comparison with the characteristiclength scale of usual segmental motion even at a temperature below its bulk glass transition temperature, T_g^b. This isconsistent with our previous results that the surface glass transition temperature is much lower than the corresponding T_g^b.Also, it was experimentally revealed that there was a gradient of molecular motion in the surface region.展开更多
We investigate gate-regulated transition temperatures for electron hopping behaviours through discrete ionized dopant atoms in silicon junctionless nanowire transistors.We demonstrate that the localization length of t...We investigate gate-regulated transition temperatures for electron hopping behaviours through discrete ionized dopant atoms in silicon junctionless nanowire transistors.We demonstrate that the localization length of the wave function in the spatial distribution is able to be manipulated by the gate electric field.The transition temperatures regulated as the function of the localization length and the density of states near the Fermi energy level allow us to understand the electron hopping behaviours under the influence of thermal activation energy and Coulomb interaction energy.This is useful for future quantum information processing by single dopant atoms in silicon.展开更多
A functional integral approach (FIA) is introduced to calculate the transition temperature of a uniform imperfect Bose gas. With this approach we find that the transition temperature is higher than that of the corresp...A functional integral approach (FIA) is introduced to calculate the transition temperature of a uniform imperfect Bose gas. With this approach we find that the transition temperature is higher than that of the corresponding ideal gas. We obtain the expression of the transition temperature shift as , where n is the density of particle number and a is the scattering length. The result has never been reported in the literature.展开更多
The bi-functional carbazole-based photorefractive polyphosphazenes with different content of C_（60）-doped were fabricated. The glass transition temperature（T_g） of these polymer composite materials was determined ...The bi-functional carbazole-based photorefractive polyphosphazenes with different content of C_（60）-doped were fabricated. The glass transition temperature（T_g） of these polymer composite materials was determined using a differential scanning calorimetric（DSC） method. According to the DSC measurement results with different heating rates, the variation of T_g and the active energy of glass transition（E_g） were analyzed in detail. The analysis results indicate that the transition region shifts to higher temperatures with increasing heating rate, and C_（60） content（below 1.0 wt%） can influence the T_g of photorefractive polyphosphazenes. The T_g first increases and then decreases with the C_（60） content（below 1.0 wt%）. The probable causes of the influence of C_（60） on T_g was proposed.展开更多
In order to predict the mechanical performance of the polyvinyl chloride （PVC） at a high operating temperature, a series of short-term tensile creep tests （one- tenth of the physical aging time） of the PVC are car...In order to predict the mechanical performance of the polyvinyl chloride （PVC） at a high operating temperature, a series of short-term tensile creep tests （one- tenth of the physical aging time） of the PVC are carried out at 63 ℃ with a small constant stress by a dynamic mechanical analyzer （DMA）. The Struik-Kohlrausch （SK） formula and Struik shifting methods are used to describe these creep data for various physical aging time. A new phenomenological model based on the multiple relaxation mechanisms of an amorphous polymer is developed to quantitatively characterize the SK parameters （the initial creep compliance, the characteristic retardation time, and the shape factor） determined by the aging time. It is shown that the momentary creep compliance curve of the PVC at 63℃ can be very well fitted by the SK formula for each aging time. However, the SK parameters for the creep curves are not constant during the aging process at the elevated temperatures, and the evolution of these parameters and the creep rate versus aging time curves at the double logarithmic coordinafes have shown a nonlinear phenomenon. Moreover, the creep master curves obtained by the superposition with the Struik shifting methods are unsatisfactory in such a case. Finally, the predicted results calculated from the present model incorporating with the SK formula are in excellent agreement with the creep experimental data for the PVC isothermally aged at the temperature relatively close to the glass transition temperature.展开更多
A three-descriptor quantitative structure-property relationship （QSPR） model, based on the support vector machine （SVM） algorithm, was constructed to predict the glass transition temperatures （Tgs） ofpolyarylate...A three-descriptor quantitative structure-property relationship （QSPR） model, based on the support vector machine （SVM） algorithm, was constructed to predict the glass transition temperatures （Tgs） ofpolyarylates with complex structures. A total of 50 polyarylates were randomly divided into three sets, viz., the training set （30 polymers）, validation set （10 polymers） and prediction set （10 polymers）. By adjusting various parameters by trial and error, the final optimum SVM model based on Austin Model 1 （AM1） calculation is a polynomial kernel with the parameters C of 100, ε of 1.00E-05 and d of 2. The root-mean-square （RMS） errors obtained from the training set, validation set and prediction set are 19.4, 12.8 and 15.5 K, respectively. Research results show that the proposed SVM model has better statistical quality than the previous models. Thus, applying the SVM algorithm to predict Tgs of polymers is feasible.展开更多
In this paper, an artificial neural network model is adopted to study the glass transition temperature of polymers. In our artificial neural networks, the input nodes are the characteristic ratio C-infinity, the avera...In this paper, an artificial neural network model is adopted to study the glass transition temperature of polymers. In our artificial neural networks, the input nodes are the characteristic ratio C-infinity, the average molecular weight M-e between entanglement points and the molecular weight M-mon of repeating unit. The output node is the glass transition temperature T-g, and the number of the hidden layer is 6. We found that the artificial neural network simulations are accurate in predicting the outcome for polymers for which it is not trained. The maximum relative error for predicting of the glass transition temperature is 3.47%, and the overall average error is only 2.27%. Artificial neural networks may provide some new ideas to investigate other properties of the polymers.展开更多
Systemic measurements show that there is no 3D to 2D crossover in the reduction of the superconducting transition temperature Tc in Nb thin films. This result is consistent with all previous measurements while it is c...Systemic measurements show that there is no 3D to 2D crossover in the reduction of the superconducting transition temperature Tc in Nb thin films. This result is consistent with all previous measurements while it is contrary to the prevailing understanding based on the interplay between proximity, localization, and lifetime broadening. Our study indicates that the decrease of Tc can be interpreted by the combined effects of electron-phonon coupling parameter λ and the defect scattering rate pw, being uniquely determined by their ratio λ/ρw. Other factors such as film thickness and irradiation do not produce additional effects beyond these two parameters.展开更多
Understanding of the mechanisms of neural phase transitions is crucial for clarifying cognitive processes in the brain. We investigate a neural oscillator that undergoes different bifurcation transitions from the big ...Understanding of the mechanisms of neural phase transitions is crucial for clarifying cognitive processes in the brain. We investigate a neural oscillator that undergoes different bifurcation transitions from the big saddle homoclinic orbit type to the saddle node on an invariant circle type, and the saddle node on an invariant circle type to the small saddle homoclinic orbit type. The bifurcation transitions are accompanied by an increase in thermodynamic temperature that affects the voltage-gated ion channel in the neural oscillator. We show that nonlinear and thermodynamical mechanisms are responsible for different switches of the frequency in the neural oscillator. We report a dynamical role of the phase response curve in switches of the frequency, in terms of slopes of frequency-temperature curve at each bifurcation transition. Adopting the transition state theory of voltagegated ion channel dynamics, we confirm that switches of the frequency occur in the first-order phase transition temperature states and exhibit different features of their potential energy derivatives in the ion channel. Each bifurcation transition also creates a discontinuity in the Arrhenius plot used to compute the time constant of the ion channel.展开更多
Molecule dynamics simulation was used on HPT(2,3,6,7,10,11-hexa-n-pentyloxytriphenylene), which is a discotic Liquid crystal. From analyzing the energy and displacement varying with the temperature, the phase transiti...Molecule dynamics simulation was used on HPT(2,3,6,7,10,11-hexa-n-pentyloxytriphenylene), which is a discotic Liquid crystal. From analyzing the energy and displacement varying with the temperature, the phase transition temperature of PM6MPP can be predicted. The deviations of T-g, T-m and T-i due to the MD time scale are small enough that it should be possibly used to predict the material properties especially when more powerful computers are available.展开更多
Despite the great leap forward perovskite solar cells(PSCs)have achieved in power conversion efficiency,the device instability remains one of the major problems plaguing its commercialization.Dopant-free hole transpor...Despite the great leap forward perovskite solar cells(PSCs)have achieved in power conversion efficiency,the device instability remains one of the major problems plaguing its commercialization.Dopant-free hole transport material(HTM)has been widely studied as an important strategy to improve the stability of PSCs due to its avoidance of moisture-sensitive dopants and cumbersome doping process.In this work,a series of dopant-free HTMs L1F,L2F and L3F based on D-A-π-A-D configuration were synthesized through two steps of reaction.L3F presents a high glass transition temperature of 1800C and thermal decomposition temperature of 4480C.Notably,electron paramagnetic resonance signals of L1F,L2F and L3F powders indicate the open-shell quinoidal diradical resonance structure in their aggregation state due to aggregation-induced radical effect.All these HTMs present higher hole mobility than dopant-free Spiro-OMeTAD,and the dopant-free L3F-based PSC device achieves the highest power conversion efficiency of 17.6%among them.In addition,due to the high hydrophobic properties of L1F,L2F and L3F,the perovskite films spin-coated with these HTMs exhibit higher humidity stability than doped SpiroOMeTAD.These results demonstrate a promising design strategy for high glass transition temperature dopant-free hole transport material.The open-shell quinoid-radical organic semiconductors are not rational candidates for dopant-free HTMs for PSC devices.展开更多
The safety and longevity of small modular reactors are affected by reactor pressure vessels,which are complex integral components made of SA508 Gr.3 low-alloy steel.In this study,the impacts of heat accumulation on th...The safety and longevity of small modular reactors are affected by reactor pressure vessels,which are complex integral components made of SA508 Gr.3 low-alloy steel.In this study,the impacts of heat accumulation on the microstructural and mechanical characteristics(tensile properties and Charpy V-notched impact energy)of SA508 Gr.3 steel fabricated using laser powder-directed energy deposition were investigated.Rectangular samples were prepared using long raster and short raster scanning strate-gies for changing heat buildup,and the mechanical tests were conducted depending on build direction.The time-temperature profile measured at a fixed point in the long raster sample showed a lower max-imum temperature and a higher cooling rate,indicating lower heat accumulation compared to that of the short raster sample.In each build direction,the yield strength of the long raster sample was 45.8%-60.5%higher and its ductile-brittle transition temperature was 76.8-103.8℃ lower than that of the short raster sample.Additionally,compared to conventionally made samples and without requiring heat treat-ment,the long raster sample exhibited over a 45%increase in yield strength and a 22.7℃ reduction in the ductile-brittle transition temperature.The superior combination in long raster samples is induced by smaller effective grain size,smaller cementite,and a higher pre-existing dislocation density.The re-sults emphasize the importance of controlling heat accumulation throughout the additive manufacturing process and provide valuable insights into the use of additive manufacturing for manufacturing reactor pressure vessels in the nuclear industry.展开更多
Enhancing the semiconductor-metal phase transition temperature(TSMT)of VO_(2) is of great consequence for further exploring the potential applications of VO_(2) at elevated temperatures.In this study,Ge^(4+)-doped VO_...Enhancing the semiconductor-metal phase transition temperature(TSMT)of VO_(2) is of great consequence for further exploring the potential applications of VO_(2) at elevated temperatures.In this study,Ge^(4+)-doped VO_(2)(Ge_(x)V_(1-x)O_(2))samples were prepared by the hydrothermal and annealing approach.X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM),differential scanning calorimetry(DSC)and resistivity-temperature(R-T)analyses were used to investigate the influence of Ge doping on the lattice structures and phase transition properties of Ge_(x)V_(1-x)O_(2) samples.We found that the lattice parameter of Ge_(x)V_(1-x)O_(2) decreased with the Ge concentration increasing from 2 at%to 18 at%,which was further supported by density functional theory(DFT)-based first-principle simulations.TSMT firstly increased from 64.5 to 73.0℃ at 8 at% Ge and then decreased to 71.5℃ at higher Ge concentration.Furthermore,DFT analysis revealed that the impact of lattice distortion induced by Ge doping rather than the changes in electronic structure is more pronounced on modulating TSMT of Ge_(x)V_(1-x)O_(2).The present work has pointed out the direction that the TSMT could be enhanced and illustrated the physical reason behind the regulation of TSMT in ionsdoped VO_(2) systems.展开更多
基金The project was support by the Natural Science Foundation of University of Anhui Province (No. 2006KJ156B)
文摘Structural parameters of 22 polyacrylic compounds were computed at two levels using Hartree-Fock and DFT methods. Based on the experimental data of glass transition temperature （Tg）, four-parameter （energy of the lowest unoccupied molecular orbital （ELoMO）, the highest positive charge （Qmax^＋）, dipole moments（μ） and the next highest occupied molecular orbital （ENLOMO）） dependent equations were developed using structural parameters as theoretical descriptors. Especially, Tg dependent equation calculated at the HF/6-31G（d） level is more advantageous than others in view of their correlation and predictive abilities. This dependent equation was validated by variance inflation factors （VIF） and t-test methods.
基金Projects(51404183,51504177)supported by the National Natural Science Foundation of China。
文摘The VO2 powders were prepared by hydrothermal synthesis.The effects of heat treatment conditions and Y-doping on the structure and phase transition temperature of VO2 were studied.The XRD,SEM and TEM results show that the heat treatment temperature has a significant effect on the crystal transformation of VO2 precursor.Increasing temperature is conducive to the transformation of precursor VO2(B)to ultrafine VO2(M).The Y-doping affects the structure of VO2.Y^3+can occupy the lattice position of V4+to form YVO4 solid solution,which can increase the cell parameters of VO2.Due to the lattice deformation caused by Y-doping,the aggregation of particles is prevented,and the grain is refined obviously.DSC curves show that Y-doping can reduce the phase transition temperature of VO2(M).After adding 9 at.%Y,the phase transition temperature can be reduced from 68.3 to 61.3℃.
基金supported by the National Basic Research Program of China (No. 2006CB601005)the National High Technology Research and Development Program of China (No. 2009AA032401)+2 种基金the National Natural Science Foundation of China (Nos. 50771003 and 50802004)the Beijing Municipal Natural Science Foundation (No. 2092006)the Program for New Century Excellent Talents in University of Ministry of Education of China (No. 39009001201002)
文摘The superconductivity of iron-based superconductor SmO 0.7 F 0.2 FeAs was investigated. The SmO 0.7 F 0.2 FeAs sample was prepared by the two-step solid-state reaction method. The onset resistivity transition temperature is as high as 56.5 K. X-ray diffraction （XRD） results show that the lattice parameters a and c are 0.39261 and 0.84751 nm, respectively. Furthermore, the global J c was more than 2.3 × 10 5 A/cm 2 at T = 10 K and H = 9 T, which was calculated by the formula of J c = 20ΔM/[a（1-a/（3b））]. The upper critical fields, H c2 ≈ 256 T （T = 0 K）, was determined according to the Werthamer-Helfand-Hohenberg formula, indicating that the SmO 0.7 F 0.2 FeAs was a superconductor with a very promising application.
文摘On the basis of analysis of low carbon steel fracture macro-features and micro-processes at low temperature,the definition was given of the characteristic transition temperature of brittleness,T_(pm),and its physical meaning was expounded.Discussion was carried out of phys- ical characteristic of variation at T_(pm) in respect of the fracture toughness and property of crack arrest.In addition,research was made on the application of T_(pm),which can give infor- mation about the transition of the fracture toughness,the property of crack arrest and critical crack size,to estimation the brittleness of low carbon steel at low temperatures.
文摘The effect of Al content on the ductile-brittle transition temperature of Al-Si coating and the effect of fracture behaviour.of the Al-Si coating on the fatigue properties of Ni-base superallovs have been investigated to propose the theoretical basis of search for an optimum of mechanical properties of the high temperature coating on Ni-base alloys.
基金the National Natural Science Foundation of China(Grant Nos.11804031 and 11904297)the Scientific Research Project of Education Department of Hubei Province,China(Grant No.Q20191301)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.SWUKT22049)the Chongqing Talent Plan for Young Top Notch Talents,China(Grant No.202005007)。
文摘High pressure is an effective method to induce structural and electronic changes,creating novel high-pressure structures with excellent physical and chemical properties.Herein,we investigate the structural phase transition of hafnium dihydrogen(HfH2)in a pressure range of 0 GPa-500 GPa through the first-principles calculations and the crystal structure analysis by particle swarm optimization(CALYPSO)code.The high-pressure phase transition sequence of HfH2is I4/mmm→Cmma→P-3m1 and the two phase transition pressure points are 220.21 GPa and 359.18 GPa,respectively.A newly trigonal P-3m1 structure with 10-fold coordination first appears as an energy superior structure under high pressure.These three structures are all metallic with the internal ionic bonding of Hf and H atoms.Moreover,the superconducting transition temperature(Tc)values of Cmma at 300 GPa and P-3m1 at 500 GPa are 3.439 K and 19.737 K,respectively.Interestingly,the superconducting transition temperature of the P-3m1 structure presents an upward trend with the pressure rising,which can be attributed to the increase of electron-phonon coupling caused by the enhanced Hf-d electronic density of states at Fermi level under high pressure.
基金This work was in part supported by a Gran-in-Aid for Scientific Research (A)(#13355034) from the Ministry of Education, Science, Sports, and Culture, Japan.
文摘In this study, it was examined whether the dynamics of polymer chains at a surface is different from that in thebulk, and if so, to what extent they differ in terms of surface glass transition temperature and diffusion coefficient. Obtainedresults clearly indicate that surface chains can travel for a relatively large distance in comparison with the characteristiclength scale of usual segmental motion even at a temperature below its bulk glass transition temperature, T_g^b. This isconsistent with our previous results that the surface glass transition temperature is much lower than the corresponding T_g^b.Also, it was experimentally revealed that there was a gradient of molecular motion in the surface region.
基金supported by the National Key R&D Program of China(Grant No.2016YFA0200503)。
文摘We investigate gate-regulated transition temperatures for electron hopping behaviours through discrete ionized dopant atoms in silicon junctionless nanowire transistors.We demonstrate that the localization length of the wave function in the spatial distribution is able to be manipulated by the gate electric field.The transition temperatures regulated as the function of the localization length and the density of states near the Fermi energy level allow us to understand the electron hopping behaviours under the influence of thermal activation energy and Coulomb interaction energy.This is useful for future quantum information processing by single dopant atoms in silicon.
文摘A functional integral approach (FIA) is introduced to calculate the transition temperature of a uniform imperfect Bose gas. With this approach we find that the transition temperature is higher than that of the corresponding ideal gas. We obtain the expression of the transition temperature shift as , where n is the density of particle number and a is the scattering length. The result has never been reported in the literature.
基金the National Science Foundation of China(No.11174258)the Development Foundation of China Academy of Engineering Physics(No.2013A0302016)
文摘The bi-functional carbazole-based photorefractive polyphosphazenes with different content of C_（60）-doped were fabricated. The glass transition temperature（T_g） of these polymer composite materials was determined using a differential scanning calorimetric（DSC） method. According to the DSC measurement results with different heating rates, the variation of T_g and the active energy of glass transition（E_g） were analyzed in detail. The analysis results indicate that the transition region shifts to higher temperatures with increasing heating rate, and C_（60） content（below 1.0 wt%） can influence the T_g of photorefractive polyphosphazenes. The T_g first increases and then decreases with the C_（60） content（below 1.0 wt%）. The probable causes of the influence of C_（60） on T_g was proposed.
基金Project supported by the National Natural Science Foundation of China (Nos. 10672095 and 11072137)the Shanghai Leading Academic Discipline Project (No. S30106)
文摘In order to predict the mechanical performance of the polyvinyl chloride （PVC） at a high operating temperature, a series of short-term tensile creep tests （one- tenth of the physical aging time） of the PVC are carried out at 63 ℃ with a small constant stress by a dynamic mechanical analyzer （DMA）. The Struik-Kohlrausch （SK） formula and Struik shifting methods are used to describe these creep data for various physical aging time. A new phenomenological model based on the multiple relaxation mechanisms of an amorphous polymer is developed to quantitatively characterize the SK parameters （the initial creep compliance, the characteristic retardation time, and the shape factor） determined by the aging time. It is shown that the momentary creep compliance curve of the PVC at 63℃ can be very well fitted by the SK formula for each aging time. However, the SK parameters for the creep curves are not constant during the aging process at the elevated temperatures, and the evolution of these parameters and the creep rate versus aging time curves at the double logarithmic coordinafes have shown a nonlinear phenomenon. Moreover, the creep master curves obtained by the superposition with the Struik shifting methods are unsatisfactory in such a case. Finally, the predicted results calculated from the present model incorporating with the SK formula are in excellent agreement with the creep experimental data for the PVC isothermally aged at the temperature relatively close to the glass transition temperature.
基金supported by the Open Project Program of Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education,China (No.10HJYH06)
文摘A three-descriptor quantitative structure-property relationship （QSPR） model, based on the support vector machine （SVM） algorithm, was constructed to predict the glass transition temperatures （Tgs） ofpolyarylates with complex structures. A total of 50 polyarylates were randomly divided into three sets, viz., the training set （30 polymers）, validation set （10 polymers） and prediction set （10 polymers）. By adjusting various parameters by trial and error, the final optimum SVM model based on Austin Model 1 （AM1） calculation is a polynomial kernel with the parameters C of 100, ε of 1.00E-05 and d of 2. The root-mean-square （RMS） errors obtained from the training set, validation set and prediction set are 19.4, 12.8 and 15.5 K, respectively. Research results show that the proposed SVM model has better statistical quality than the previous models. Thus, applying the SVM algorithm to predict Tgs of polymers is feasible.
基金This research was financially supported by NSFC (No. 29874012) and the Special Funds for Major State Basic Research Projects (95-12 and G1999064800).
文摘In this paper, an artificial neural network model is adopted to study the glass transition temperature of polymers. In our artificial neural networks, the input nodes are the characteristic ratio C-infinity, the average molecular weight M-e between entanglement points and the molecular weight M-mon of repeating unit. The output node is the glass transition temperature T-g, and the number of the hidden layer is 6. We found that the artificial neural network simulations are accurate in predicting the outcome for polymers for which it is not trained. The maximum relative error for predicting of the glass transition temperature is 3.47%, and the overall average error is only 2.27%. Artificial neural networks may provide some new ideas to investigate other properties of the polymers.
基金Supported by the National Natural Science Foundation of China under Grant No 11104331the National Basic Research Program of China under Grant No 2011CB921702
文摘Systemic measurements show that there is no 3D to 2D crossover in the reduction of the superconducting transition temperature Tc in Nb thin films. This result is consistent with all previous measurements while it is contrary to the prevailing understanding based on the interplay between proximity, localization, and lifetime broadening. Our study indicates that the decrease of Tc can be interpreted by the combined effects of electron-phonon coupling parameter λ and the defect scattering rate pw, being uniquely determined by their ratio λ/ρw. Other factors such as film thickness and irradiation do not produce additional effects beyond these two parameters.
基金Supported by JST,CREST,and JSPS KAKENHI under Grant No 15H05919
文摘Understanding of the mechanisms of neural phase transitions is crucial for clarifying cognitive processes in the brain. We investigate a neural oscillator that undergoes different bifurcation transitions from the big saddle homoclinic orbit type to the saddle node on an invariant circle type, and the saddle node on an invariant circle type to the small saddle homoclinic orbit type. The bifurcation transitions are accompanied by an increase in thermodynamic temperature that affects the voltage-gated ion channel in the neural oscillator. We show that nonlinear and thermodynamical mechanisms are responsible for different switches of the frequency in the neural oscillator. We report a dynamical role of the phase response curve in switches of the frequency, in terms of slopes of frequency-temperature curve at each bifurcation transition. Adopting the transition state theory of voltagegated ion channel dynamics, we confirm that switches of the frequency occur in the first-order phase transition temperature states and exhibit different features of their potential energy derivatives in the ion channel. Each bifurcation transition also creates a discontinuity in the Arrhenius plot used to compute the time constant of the ion channel.
文摘Molecule dynamics simulation was used on HPT(2,3,6,7,10,11-hexa-n-pentyloxytriphenylene), which is a discotic Liquid crystal. From analyzing the energy and displacement varying with the temperature, the phase transition temperature of PM6MPP can be predicted. The deviations of T-g, T-m and T-i due to the MD time scale are small enough that it should be possibly used to predict the material properties especially when more powerful computers are available.
基金financially supported by the Natural Science Foundation of China(Nos.51973063 and 22375065)。
文摘Despite the great leap forward perovskite solar cells(PSCs)have achieved in power conversion efficiency,the device instability remains one of the major problems plaguing its commercialization.Dopant-free hole transport material(HTM)has been widely studied as an important strategy to improve the stability of PSCs due to its avoidance of moisture-sensitive dopants and cumbersome doping process.In this work,a series of dopant-free HTMs L1F,L2F and L3F based on D-A-π-A-D configuration were synthesized through two steps of reaction.L3F presents a high glass transition temperature of 1800C and thermal decomposition temperature of 4480C.Notably,electron paramagnetic resonance signals of L1F,L2F and L3F powders indicate the open-shell quinoidal diradical resonance structure in their aggregation state due to aggregation-induced radical effect.All these HTMs present higher hole mobility than dopant-free Spiro-OMeTAD,and the dopant-free L3F-based PSC device achieves the highest power conversion efficiency of 17.6%among them.In addition,due to the high hydrophobic properties of L1F,L2F and L3F,the perovskite films spin-coated with these HTMs exhibit higher humidity stability than doped SpiroOMeTAD.These results demonstrate a promising design strategy for high glass transition temperature dopant-free hole transport material.The open-shell quinoid-radical organic semiconductors are not rational candidates for dopant-free HTMs for PSC devices.
基金supported by the National Research Foundation of the Ministry of Science and ICT(MSIT)of the Republic of Korea(grant No.2022M3H4A1A02076759)also supported financially by the Korea Atomic Energy Research Institute R&D program(Con-tract No.524590-24).
文摘The safety and longevity of small modular reactors are affected by reactor pressure vessels,which are complex integral components made of SA508 Gr.3 low-alloy steel.In this study,the impacts of heat accumulation on the microstructural and mechanical characteristics(tensile properties and Charpy V-notched impact energy)of SA508 Gr.3 steel fabricated using laser powder-directed energy deposition were investigated.Rectangular samples were prepared using long raster and short raster scanning strate-gies for changing heat buildup,and the mechanical tests were conducted depending on build direction.The time-temperature profile measured at a fixed point in the long raster sample showed a lower max-imum temperature and a higher cooling rate,indicating lower heat accumulation compared to that of the short raster sample.In each build direction,the yield strength of the long raster sample was 45.8%-60.5%higher and its ductile-brittle transition temperature was 76.8-103.8℃ lower than that of the short raster sample.Additionally,compared to conventionally made samples and without requiring heat treat-ment,the long raster sample exhibited over a 45%increase in yield strength and a 22.7℃ reduction in the ductile-brittle transition temperature.The superior combination in long raster samples is induced by smaller effective grain size,smaller cementite,and a higher pre-existing dislocation density.The re-sults emphasize the importance of controlling heat accumulation throughout the additive manufacturing process and provide valuable insights into the use of additive manufacturing for manufacturing reactor pressure vessels in the nuclear industry.
基金financially supported by the Natural Science Foundation of Ningxia(No.2020AAC03005)the Western Light Foundation of the Chinese Academy of Sciences。
文摘Enhancing the semiconductor-metal phase transition temperature(TSMT)of VO_(2) is of great consequence for further exploring the potential applications of VO_(2) at elevated temperatures.In this study,Ge^(4+)-doped VO_(2)(Ge_(x)V_(1-x)O_(2))samples were prepared by the hydrothermal and annealing approach.X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM),differential scanning calorimetry(DSC)and resistivity-temperature(R-T)analyses were used to investigate the influence of Ge doping on the lattice structures and phase transition properties of Ge_(x)V_(1-x)O_(2) samples.We found that the lattice parameter of Ge_(x)V_(1-x)O_(2) decreased with the Ge concentration increasing from 2 at%to 18 at%,which was further supported by density functional theory(DFT)-based first-principle simulations.TSMT firstly increased from 64.5 to 73.0℃ at 8 at% Ge and then decreased to 71.5℃ at higher Ge concentration.Furthermore,DFT analysis revealed that the impact of lattice distortion induced by Ge doping rather than the changes in electronic structure is more pronounced on modulating TSMT of Ge_(x)V_(1-x)O_(2).The present work has pointed out the direction that the TSMT could be enhanced and illustrated the physical reason behind the regulation of TSMT in ionsdoped VO_(2) systems.
