Two-dimensional(2D)fully compensated collinear magnetic materials ofer signifcant advantages for spintronic applications,including robustness against magnetic feld perturbations,no stray felds,and ultrafast dynamics.A...Two-dimensional(2D)fully compensated collinear magnetic materials ofer signifcant advantages for spintronic applications,including robustness against magnetic feld perturbations,no stray felds,and ultrafast dynamics.Among these materials,fully compensated ferrimagnets are particularly promising due to their unique characteristics such as the magneto-optical efect,completely spin-polarized currents,and the anomalous Hall efect.We performed a structural search on 2D unconventional stoichiometric Cr-I crystals using a global optimization algorithm.The most stable CrI-P21/m monolayer is a fully compensated ferrimagnetic semiconductor with a band gap of 1.57 eV and a high magnetic transition temperature of 592 K.The spontaneous spin splitting in CrI-P21/m originates from the inequivalent local coordination environments of Cr^(1)and Cr^(2)ions,yielding a mismatch in their 3d orbitals splitting.Notably,carrier doping at a concentration of 0.01 electrons or holes per atom enables reversible spin polarization,generating a fully spin-polarized current in CrI-P21/m.This performance makes it a highly promising candidate for spintronic devices.Our fndings not only provide a structural paradigm for discovering fully compensated ferrimagnets but also open a new avenue for designing zero-moment magnetic materials with intrinsic spin splitting.展开更多
Recent discovery of high transition temperature superconductivity in La_(3)Ni_(2)O_(7) has sparked renewed theoretical and experimental interests in unconventional superconductivity. It is crucial to understand the in...Recent discovery of high transition temperature superconductivity in La_(3)Ni_(2)O_(7) has sparked renewed theoretical and experimental interests in unconventional superconductivity. It is crucial to understand the influence of various factors on its superconductivity. By refining the determinant quantum Monte Carlo algorithm, we characterize the parameter dependence of the superconducting transition temperature within a bilayer Hubbard model, which is sign-problem-free at arbitrary filling. A striking feature of this model is its similarity to the bilayer nickelate-based superconductor La_(3)Ni_(2)O_(7), where superconductivity emerges from the bilayer NiO_(2) planes.We find that interlayer spin-exchange J is critical to interlayer pairing, and that on-site interaction U contributes negatively to superconductivity at low doping levels but positively at high doping levels. Our findings can provide a reference for the next step in theoretical research on nickelate-based superconductors.展开更多
Machine learning(ML)has emerged as a powerful tool for predicting polymer properties,including glass transition temperature(Tg),which is a critical factor influencing polymer applications.In this study,a dataset of po...Machine learning(ML)has emerged as a powerful tool for predicting polymer properties,including glass transition temperature(Tg),which is a critical factor influencing polymer applications.In this study,a dataset of polymer structures and their Tg values were created and represented as adjacency matrices based on molecular graph theory.Four key structural descriptors,flexibility,side chain occupancy length,polarity,and hydrogen bonding capacity,were extracted and used as inputs for ML models:Extra Trees(ET),Random Forest(RF),Gaussian Process Regression(GPR),and Gradient Boosting(GB).Among these,ET and GPR achieved the highest predictive performance,with R2 values of 0.97,and mean absolute errors(MAE)of approximately 7–7.5 K.The use of these extracted features significantly improved the prediction accuracy compared to previous studies.Feature importance analysis revealed that flexibility had the strongest influence on Tg,followed by side-chain occupancy length,hydrogen bonding,and polarity.This work demonstrates the potential of data-driven approaches in polymer science,providing a fast and reliable method for Tg prediction that does not require experimental inputs.展开更多
The reactor pressure vessel(RPV)is susceptible to brittle fracture due to the influence of ion irradiation and high temperature,which presents a significant risk to the safe operation of nuclear reactors.It has been d...The reactor pressure vessel(RPV)is susceptible to brittle fracture due to the influence of ion irradiation and high temperature,which presents a significant risk to the safe operation of nuclear reactors.It has been demonstrated that pulsed electric current can effectively address the issue of embrittlement in RPV steel.However,the relationship between pulse parameters(duty ratio,frequency,current,and time)and the effectiveness of pulse current processing has not been systematically studied.The application of machine learning methods enables autonomous exploration and learning of the relationship between data.Consequently,this study proposes a machine learning method based on the random forest model to establish the relationship between the parameters of electrical pulses and the repair effect of RPV steel.A generative adversarial network is employed to enhance data diversity and scalability,while a particle swarm optimization algorithm is utilized to optimize the initialization weights and biases of the random forest model,aiming to improve the model’s fitting ability and training performance.The results indicate that the coefficient of determination R-square(R^(2)),root mean squared error and mean absolute error values are 0.934,0.045,and 0.036,respectively,suggesting that the model has the potential to predict the performance recovery of RPV steel after pulsed electric field treatment.The prediction of the impact of pulse current parameters on the repair effect will help to enhance and optimize the repair process,thereby providing a scientific basis for pulse current repair processing.展开更多
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
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
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
The component activity of Mn in Fe-C-Mn system as well as the component activities of C and Si in Fe-C-Si system was predicted by applying the pseudo-multicomponent approach of the molecular interaction volume model ...The component activity of Mn in Fe-C-Mn system as well as the component activities of C and Si in Fe-C-Si system was predicted by applying the pseudo-multicomponent approach of the molecular interaction volume model （MIVM） and the Wagner interaction parameter formalism （WIPF） respectively. The average relative errors between the predicted values of MIVM and the experimental data for the three components were 4.5 0%, 17.0% and 13.0 %, respectively, and those between the calculation results of the WIPF and the experimental data were 18.0K for Mn, 9.0% for C and 27.0% for Si. The results indicated that the MIVM method could better predict the component activity of carbonaceous iron-based solution. Based on the data in an actual blowing process, the MIVM method was applied to predict the component activities of C and V as well as the transition temperature of vanadium oxidization （TTVO） in Fe-C-V-Si quaternary iron-based solution, and a comparative analysis of the predictions against the ex- perimental data was carried out, with their average relative errors being 24.0% for C, 7.3% for V and 1.0% for TTVO respectively. On that basis, the TTVO at Panzhihua Iron and Steel （Group） Co. , Ltd. was estimated by the MIVM method and an expression that the TTVO changed with composition and temperature of iron solutions was obtained by multiple linear regression method. The research results showed that the estimated values were in good agree- ment with the practical data.展开更多
The comparative study of submerged arc welding(SAW)and laser hybrid welding(LHW)was carried out for a 690 MPa high strength steel with thickness of 20 mm.Microstructure and ductile–brittle transition temperature(DBTT...The comparative study of submerged arc welding(SAW)and laser hybrid welding(LHW)was carried out for a 690 MPa high strength steel with thickness of 20 mm.Microstructure and ductile–brittle transition temperature(DBTT)evolution in welded zone were elucidated from the aspect of crystallographic structure,particularly,digitization and visualization of 24 variants.The impact toughness of each micro zone in LHW joint is better than that of SAW,in which the DBTT of equivalent fusion line and heat-affected zone(HAZ)can reach−70 and−80℃,while that of SAW is only−50℃.LHW technology induces narrowing of the HAZ and refining of the microstructure obtained in weld metal and HAZ.Meanwhile,the austenite grain size and transformation driving force in the coarse grained heat-affected zone(CGHAZ)are reduced and increased,respectively.It makes variant selection mechanism occurring in CGHAZ of LHW dominate by close-packed plane grouping,which promotes lath bainite formation with high density of high angle grain boundary,especially block boundary dominated by V1/V2 pair.While for SAW,the lower transformation driving force inferred from the large amount of retained austenite in CGHAZ induces Bain grouping of variants,and thus triggers the brittle crack propagating straightly in granular bainite,resulting in lower impact toughness and higher DBTT.展开更多
In this work, the effect of the fullerene（C_（60）） weight fraction and PB-C_（60） interaction on the glass transition temperature（T_g） of polymer chains has been systemically investigated by adopting the united ...In this work, the effect of the fullerene（C_（60）） weight fraction and PB-C_（60） interaction on the glass transition temperature（T_g） of polymer chains has been systemically investigated by adopting the united atom model of cis-1,4-poly（butadiene）（cis-PB）. Various chain dynamics properties, such as atom translational mobility, bond/segment reorientation dynamics, torsional dynamics, conformational transition rate and dynamic heterogeneity of the cis-PB chains, are analyzed in detail. It is found that T_g could be affected by the C_（60） weight fraction due to its inhibition effect on the mobility of the cis-PB chains. However, T_g is different, which depends on different dynamics scales. Among the chain dynamics properties, T_g is the lowest from atom translational mobility, while it is the highest from the dynamic heterogeneity. In addition, T_g can be more clearly distinguished from the dynamic heterogeneity; however, the conformational transition rate seems to be not very sensitive to the C_（60） weight fraction compared with others. For pure cis-PB chains, T_g and the activation energy in this work can be compared with those of other polymers. In addition, the temperature dependence of the dynamic properties has different Arrhenius behaviors above and below T_g. The activation energy below T_g is lower than that above T_g. This work can help to understand the effect of the C_（60） on the dynamic properties and glass transition temperature of the cis-PB chains from different scales.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 strategy of a reliable transition temperature control of vanadium dioxide(VO2)is reported.Rectangular VO2 nanobeams were synthesized by a thermal chemical vapor deposition(TCVD)system.The metal-insulator transitio...The strategy of a reliable transition temperature control of vanadium dioxide(VO2)is reported.Rectangular VO2 nanobeams were synthesized by a thermal chemical vapor deposition(TCVD)system.The metal-insulator transition(MIT)temperature increases to above 380K when the TiO2 ratio of the source is 5 at.%,although the Ti source is not physically doped into VO2 nanobeams.The XPS spectra of the V 2p orbital reveal the excessive oxidation of V after the TCVD processes with a higher TiO2 ratio,indicating that the TiO2 precursor is important in the O-doping of the surface V O bonds when forming volatile Ti-O gas species.Thus,TiO2 reactants can be used as a VO2 surface chemical modifier to manipulate the MIT transition temperature and maintain a homogenous VO2 phase,which is useful for a Mott device application with a record on/off switching ratio>104 and Mott transition temperature>380 K.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
Deuteration of hydrogen-bonded phase transition crystals can increase the transition temperatures due to the isotope effect. But rare examples show the opposite trend that originates from the structural changes of the...Deuteration of hydrogen-bonded phase transition crystals can increase the transition temperatures due to the isotope effect. But rare examples show the opposite trend that originates from the structural changes of the hydrogen bond, known as the geometric H/D isotope effect. Herein, we report an organic crystal, diethylammonium hydrogen 1,4-terephthalate, exhibits a reversible structural phase transition and dielectric switching. Structural study shows the cations reside in channels formed by one-dimensional hydrogen-bonded anionic chains and undergo an order-disorder transition at around 206 K. The deuterated counterpart shows an elongation of the O…O hydrogen bond by about 0.005 A. This geometric isotope effect releases the internal pressure of the anionic host on the cation vips and results in a downward shift of the phase transition temperature by 10 K.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
基金supported by the Natural Science Foundation of Wenzhou Institute,University of Chinese Academy of Sciences(UCAS)(Grant No.WIUCASQD2023004)the National Natural Science Foundation of China(Grant Nos.12304006,12404265,and 12435001)+2 种基金the Natural Science Foundation of Shanghai,China(Grant No.23JC1401400)the Natural Science Foundation of Wenzhou(Grant No.L2023005)the Fundamental Research Funds for the Central Universities of East China University of Science and Technology。
文摘Two-dimensional(2D)fully compensated collinear magnetic materials ofer signifcant advantages for spintronic applications,including robustness against magnetic feld perturbations,no stray felds,and ultrafast dynamics.Among these materials,fully compensated ferrimagnets are particularly promising due to their unique characteristics such as the magneto-optical efect,completely spin-polarized currents,and the anomalous Hall efect.We performed a structural search on 2D unconventional stoichiometric Cr-I crystals using a global optimization algorithm.The most stable CrI-P21/m monolayer is a fully compensated ferrimagnetic semiconductor with a band gap of 1.57 eV and a high magnetic transition temperature of 592 K.The spontaneous spin splitting in CrI-P21/m originates from the inequivalent local coordination environments of Cr^(1)and Cr^(2)ions,yielding a mismatch in their 3d orbitals splitting.Notably,carrier doping at a concentration of 0.01 electrons or holes per atom enables reversible spin polarization,generating a fully spin-polarized current in CrI-P21/m.This performance makes it a highly promising candidate for spintronic devices.Our fndings not only provide a structural paradigm for discovering fully compensated ferrimagnets but also open a new avenue for designing zero-moment magnetic materials with intrinsic spin splitting.
基金supported by the National Natural Science Foundation of China (Grant Nos.12234016,12174317 for C.Wu,and 12474218 for R.Ma,Z.Fan,and T.Ma)Beijing Natural Science Foundation (Grant No.1242022 for R.Ma,Z.Fan,and T.Ma)the New Cornerstone Science Foundation。
文摘Recent discovery of high transition temperature superconductivity in La_(3)Ni_(2)O_(7) has sparked renewed theoretical and experimental interests in unconventional superconductivity. It is crucial to understand the influence of various factors on its superconductivity. By refining the determinant quantum Monte Carlo algorithm, we characterize the parameter dependence of the superconducting transition temperature within a bilayer Hubbard model, which is sign-problem-free at arbitrary filling. A striking feature of this model is its similarity to the bilayer nickelate-based superconductor La_(3)Ni_(2)O_(7), where superconductivity emerges from the bilayer NiO_(2) planes.We find that interlayer spin-exchange J is critical to interlayer pairing, and that on-site interaction U contributes negatively to superconductivity at low doping levels but positively at high doping levels. Our findings can provide a reference for the next step in theoretical research on nickelate-based superconductors.
文摘Machine learning(ML)has emerged as a powerful tool for predicting polymer properties,including glass transition temperature(Tg),which is a critical factor influencing polymer applications.In this study,a dataset of polymer structures and their Tg values were created and represented as adjacency matrices based on molecular graph theory.Four key structural descriptors,flexibility,side chain occupancy length,polarity,and hydrogen bonding capacity,were extracted and used as inputs for ML models:Extra Trees(ET),Random Forest(RF),Gaussian Process Regression(GPR),and Gradient Boosting(GB).Among these,ET and GPR achieved the highest predictive performance,with R2 values of 0.97,and mean absolute errors(MAE)of approximately 7–7.5 K.The use of these extracted features significantly improved the prediction accuracy compared to previous studies.Feature importance analysis revealed that flexibility had the strongest influence on Tg,followed by side-chain occupancy length,hydrogen bonding,and polarity.This work demonstrates the potential of data-driven approaches in polymer science,providing a fast and reliable method for Tg prediction that does not require experimental inputs.
基金financially supported by the National Natural Science Foundation of China(U21B2082,52474410)the National Key R&D Program of China(2023YFB3709903,2020 YFA0714900)+5 种基金the Key R&D Program of Shandong Province,China(2023CXGC010406)the Scientific Research Special Project for First-Class Disciplines in Inner Mongolia Autonomous Region(YLXKZXNKD-001)the Natural Science Foundation of Inner Mongolia Autonomous Region of China(2024ZD06)the Technology Support Project for the Construction of Major Innovation Platforms in Inner Mongolia Autonomous Region(XM2024XTGXQ16)the Beijing Municipal Natural Science Foundation(2222065)the Fundamental Research Funds for the Central Universities(FRF-TP-22-02C2).
文摘The reactor pressure vessel(RPV)is susceptible to brittle fracture due to the influence of ion irradiation and high temperature,which presents a significant risk to the safe operation of nuclear reactors.It has been demonstrated that pulsed electric current can effectively address the issue of embrittlement in RPV steel.However,the relationship between pulse parameters(duty ratio,frequency,current,and time)and the effectiveness of pulse current processing has not been systematically studied.The application of machine learning methods enables autonomous exploration and learning of the relationship between data.Consequently,this study proposes a machine learning method based on the random forest model to establish the relationship between the parameters of electrical pulses and the repair effect of RPV steel.A generative adversarial network is employed to enhance data diversity and scalability,while a particle swarm optimization algorithm is utilized to optimize the initialization weights and biases of the random forest model,aiming to improve the model’s fitting ability and training performance.The results indicate that the coefficient of determination R-square(R^(2)),root mean squared error and mean absolute error values are 0.934,0.045,and 0.036,respectively,suggesting that the model has the potential to predict the performance recovery of RPV steel after pulsed electric field treatment.The prediction of the impact of pulse current parameters on the repair effect will help to enhance and optimize the repair process,thereby providing a scientific basis for pulse current repair processing.
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.
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.
基金Item Sponsored by National Natural Science Foundation of China(51090381,50764006)
文摘The component activity of Mn in Fe-C-Mn system as well as the component activities of C and Si in Fe-C-Si system was predicted by applying the pseudo-multicomponent approach of the molecular interaction volume model （MIVM） and the Wagner interaction parameter formalism （WIPF） respectively. The average relative errors between the predicted values of MIVM and the experimental data for the three components were 4.5 0%, 17.0% and 13.0 %, respectively, and those between the calculation results of the WIPF and the experimental data were 18.0K for Mn, 9.0% for C and 27.0% for Si. The results indicated that the MIVM method could better predict the component activity of carbonaceous iron-based solution. Based on the data in an actual blowing process, the MIVM method was applied to predict the component activities of C and V as well as the transition temperature of vanadium oxidization （TTVO） in Fe-C-V-Si quaternary iron-based solution, and a comparative analysis of the predictions against the ex- perimental data was carried out, with their average relative errors being 24.0% for C, 7.3% for V and 1.0% for TTVO respectively. On that basis, the TTVO at Panzhihua Iron and Steel （Group） Co. , Ltd. was estimated by the MIVM method and an expression that the TTVO changed with composition and temperature of iron solutions was obtained by multiple linear regression method. The research results showed that the estimated values were in good agree- ment with the practical data.
基金financially supported by the National Natural Science Foundation of China(No.52001023)the Special Fund for Science and Technology Project of Guangdong Province(No.SDZX2020008)the Key Research and Development Program of Shandong Province,China(No.2019JZZY020238).
文摘The comparative study of submerged arc welding(SAW)and laser hybrid welding(LHW)was carried out for a 690 MPa high strength steel with thickness of 20 mm.Microstructure and ductile–brittle transition temperature(DBTT)evolution in welded zone were elucidated from the aspect of crystallographic structure,particularly,digitization and visualization of 24 variants.The impact toughness of each micro zone in LHW joint is better than that of SAW,in which the DBTT of equivalent fusion line and heat-affected zone(HAZ)can reach−70 and−80℃,while that of SAW is only−50℃.LHW technology induces narrowing of the HAZ and refining of the microstructure obtained in weld metal and HAZ.Meanwhile,the austenite grain size and transformation driving force in the coarse grained heat-affected zone(CGHAZ)are reduced and increased,respectively.It makes variant selection mechanism occurring in CGHAZ of LHW dominate by close-packed plane grouping,which promotes lath bainite formation with high density of high angle grain boundary,especially block boundary dominated by V1/V2 pair.While for SAW,the lower transformation driving force inferred from the large amount of retained austenite in CGHAZ induces Bain grouping of variants,and thus triggers the brittle crack propagating straightly in granular bainite,resulting in lower impact toughness and higher DBTT.
基金financial supports from the start-up funding of Beijing University of Chemical Technology(BUCT)for excellent introduced talentsthe Fundamental Research Funds for the Central Universities(JD1711)
文摘In this work, the effect of the fullerene（C_（60）） weight fraction and PB-C_（60） interaction on the glass transition temperature（T_g） of polymer chains has been systemically investigated by adopting the united atom model of cis-1,4-poly（butadiene）（cis-PB）. Various chain dynamics properties, such as atom translational mobility, bond/segment reorientation dynamics, torsional dynamics, conformational transition rate and dynamic heterogeneity of the cis-PB chains, are analyzed in detail. It is found that T_g could be affected by the C_（60） weight fraction due to its inhibition effect on the mobility of the cis-PB chains. However, T_g is different, which depends on different dynamics scales. Among the chain dynamics properties, T_g is the lowest from atom translational mobility, while it is the highest from the dynamic heterogeneity. In addition, T_g can be more clearly distinguished from the dynamic heterogeneity; however, the conformational transition rate seems to be not very sensitive to the C_（60） weight fraction compared with others. For pure cis-PB chains, T_g and the activation energy in this work can be compared with those of other polymers. In addition, the temperature dependence of the dynamic properties has different Arrhenius behaviors above and below T_g. The activation energy below T_g is lower than that above T_g. This work can help to understand the effect of the C_（60） on the dynamic properties and glass transition temperature of the cis-PB chains from different scales.
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This study was supported through the National Research Foundation of Korea[NRF-2019M3F3A1A03079739 and NRF-2019R1A2C2003804]of the Ministry of Science and ICT,Republic of Korea.This study was partially supported by Leaders in Industryuniversity Cooperation+Project,supported by the Ministry of Education,Republic of Korea and by Ajou University.Minhwan Ko and Sang Yeon Lee contributed equally to this study.
文摘The strategy of a reliable transition temperature control of vanadium dioxide(VO2)is reported.Rectangular VO2 nanobeams were synthesized by a thermal chemical vapor deposition(TCVD)system.The metal-insulator transition(MIT)temperature increases to above 380K when the TiO2 ratio of the source is 5 at.%,although the Ti source is not physically doped into VO2 nanobeams.The XPS spectra of the V 2p orbital reveal the excessive oxidation of V after the TCVD processes with a higher TiO2 ratio,indicating that the TiO2 precursor is important in the O-doping of the surface V O bonds when forming volatile Ti-O gas species.Thus,TiO2 reactants can be used as a VO2 surface chemical modifier to manipulate the MIT transition temperature and maintain a homogenous VO2 phase,which is useful for a Mott device application with a record on/off switching ratio>104 and Mott transition temperature>380 K.
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financially supported by the National Natural Science Foundation of China (Nos. 21875035 and 21991144)。
文摘Deuteration of hydrogen-bonded phase transition crystals can increase the transition temperatures due to the isotope effect. But rare examples show the opposite trend that originates from the structural changes of the hydrogen bond, known as the geometric H/D isotope effect. Herein, we report an organic crystal, diethylammonium hydrogen 1,4-terephthalate, exhibits a reversible structural phase transition and dielectric switching. Structural study shows the cations reside in channels formed by one-dimensional hydrogen-bonded anionic chains and undergo an order-disorder transition at around 206 K. The deuterated counterpart shows an elongation of the O…O hydrogen bond by about 0.005 A. This geometric isotope effect releases the internal pressure of the anionic host on the cation vips and results in a downward shift of the phase transition temperature by 10 K.
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.
