Cinchoninium has emerged as a powerful scaffold with its distinctive chiral environment and diverse weak bonding interactions.This strategy has successfully enabled a series of highly reactive and selective asymmetric...Cinchoninium has emerged as a powerful scaffold with its distinctive chiral environment and diverse weak bonding interactions.This strategy has successfully enabled a series of highly reactive and selective asymmetric transformations,with umpolung Michael addition of imines being a representative example.However,the understanding of chirality control in these transformations is hindered by the diverse and directionless nature of weak bonding interactions,rendering the stereochemical model elusive.In this study,we present a mechanistic investigation of the stereochemical model and selectivity-controlling factors of the titled reaction.The addition of azaallyl anion to enal is identified as the rate-and selectivity-determining step.In this favorable addition transition state,a new catalyst-substrate binding mode is elucidated:cinchoninium binds the enal oxygen through multiple positively charged C-H bonds in the quinuclidinium core,while the position of azaallyl anion is governed by nonclassical hydrogen-bonding interactions with the peripheral phenyl C-H bonds of the catalyst.A total set of seven weak bonding interactions collectively establish a specific chiral environment that stabilizes only one out of eight possible Michael addition transition states,thus achieving the observed regio-and stereoselectivity.Subsequent titration experiments were conducted to validate the proposed weak bonding network.These mechanistic insights led to the establishment of a quantitative structure-enantioselectivity relationship through a multivariate linear regression approach.Our findings provide a comprehensive stereochemical model for understanding cinchoninium-catalyzed umpolung transformations of imines,elucidating the key functional groups responsible for the chirality control in this catalytic system.The mechanistic insights obtained serve as a rational basis for future designs of related asymmetric transformations.展开更多
Amorphous indium-gallium-zinc oxide(a-IGZO)thin films are prepared by pulsed laser deposition and fabricated into thin-film transistor(TFT)devices.In-situ x-ray photoelectron spectroscopy(XPS)illustrates that weakly b...Amorphous indium-gallium-zinc oxide(a-IGZO)thin films are prepared by pulsed laser deposition and fabricated into thin-film transistor(TFT)devices.In-situ x-ray photoelectron spectroscopy(XPS)illustrates that weakly bonded oxygen(O)atoms exist in a-IGZO thin films deposited at high O_(2) pressures,but these can be eliminated by vacuum annealing.The threshold voltage(V_(th))of the a-IGZO TFTs is shifted under positive gate bias,and the Vth shift is positively related to the deposition pressure.A temperature variation experiment in the range of 20 K-300 K demonstrates that an activation energy of 144 meV is required for the Vth shift,which is close to the activation energy required for the migration of weakly bonded O atoms in a-IGZO thin films.Accordingly,the Vth shift is attributed to the acceptor-like states induced by the accumulation of weakly bonded O atoms at the a-IGZO/SiO_(2) interface under positive gate bias.These results provide an insight into the mechanism responsible for the Vth shift of the a-IGZO TFTs and help in the production of reliable designs.展开更多
Adhesively bonded joints are widely used in modern lightweight structures due to their high strengthto-weight ratio and design flexibility.However,the reliable non-destructive evaluation of bond integrity remains a si...Adhesively bonded joints are widely used in modern lightweight structures due to their high strengthto-weight ratio and design flexibility.However,the reliable non-destructive evaluation of bond integrity remains a significant challenge.This study presents a numerical investigation of adhesively bonded joints with different adhesive properties using ultrasonic guided waves.The main focus of the investigation is to evaluate the feasibility of using guided waves to assess bond integrity,particularly for detecting challenging weak bonds.For this purpose,a theoretical analysis of dispersion curves was conducted,revealing that the S0 Lamb wave mode is significantly sensitive to variations in adhesive properties in the 300-700 kHz frequency range.Finite element modelling was used to analyse the propagation of guided waves in two scenarios:an adhesively bonded aluminum structure and a more complex configuration-adhesively bonded lap joints.The Short-Time Fourier Transform(STFT)was used to process the obtained results and determine the group velocities of guided waves.By analysing the group velocity characteristics,their dependence on the adhesive properties was identified.In the first scenario,a clear separation of S0 modes from A0 modes was observed in the STFT analysis,with a decrease in group velocity as adhesive stiffness increased.For the more complex lap joint scenario,the separation between A0 and S0 modes was less distinct.However,the analysis of the average group velocity shows a dependence of average group velocity on adhesive properties.This is similar to the first scenario.There is a decrease in average group velocity as adhesive stiffness increases.The results obtained demonstrate that guided wavebased methods have a high potential for non-destructive evaluation of adhesively bonded structures,including the detection of weak bonds.展开更多
Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coatin...Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials.In this paper,we present a first-principles calculations of the phonon transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers.Both materials possess low lattice thermal conductivity,at least two orders of magnitude lower than graphene and h-BN.The room temperature thermal conductivity of Pb_(2)SbAs(0.91 W/m K)is only a quarter of that of Pb_(2)PAs(3.88 W/m K).We analyze in depth the bonding,lattice dynamics,and phonon mode level information of these materials.Ultimately,it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures.Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb_(2)PAs and Pb_(2)SbAs,and the three-phonon scattering is sufficient to describe their anharmonicity.In this study,the thermal transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers are illuminated based on fundamental physical mechanisms,and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.展开更多
Hydraulic-electric rock fragmentation(HERF)plays a significant role in improving the efficiency of high voltage pulse rock breaking.However,the underlying mechanism of HERF remains unclear.In this study,considering th...Hydraulic-electric rock fragmentation(HERF)plays a significant role in improving the efficiency of high voltage pulse rock breaking.However,the underlying mechanism of HERF remains unclear.In this study,considering the heterogeneity of the rock,microscopic thermodynamic properties,and shockwave time domain waveforms,based on the shockwave model,digital imaging technology and the discrete element method,the cyclic loading numerical simulations of HERF is achieved by coupling electrical,thermal,and solid mechanics under different formation temperatures,confining pressure,initial peak voltage,electrode bit diameter,and loading times.Meanwhile,the HERF discharge system is conducive to the laboratory experiments with various electrical parameters and the resulting broken pits are numerically reconstructed to obtain the geometric parameters.The results show that,the completely broken area consists of powdery rock debris.In the pre-broken zone,the mineral cementation of the rock determines the transition of type CⅠcracks to type CⅡand type CⅢcracks.Furthermore,the peak pressure of the shockwave increased with initial peak voltage but decreased with electrode bit diameter,while the wave front time reduced.Moreover,increasing well depth,formation temperature and confining pressure augment and inhibit HERF,but once confining pressure surpassed the threshold of 60 MPa for 152.40,215.90,and 228.60 mm electrode bits,and 40 MPa for 309.88 mm electrode bits,HERF is promoted.Additionally,for the same kind of rock,the volume and width of the broken pit increase with higher initial peak voltage and rock fissures will promote HERF.Eventually,the electrode drill bit with a 215.90 mm diameter is more suitable for drilling pink granite.This research contributes to a better microscopic understanding of HERF and provides valuable insights for electrode bit selection,as well as the optimization of circuit parameters for HERF technology.展开更多
Lewis acid−base adducts resulting from instantaneous interactions provide a cost-effective strategy for color tuning and anticounterfeiting information.Herein,we report the construction of luminescent Lewis acid−base ...Lewis acid−base adducts resulting from instantaneous interactions provide a cost-effective strategy for color tuning and anticounterfeiting information.Herein,we report the construction of luminescent Lewis acid−base adducts via inkjet printing.Due to the unique weak coordination bond of B→N,it is feasible to construct anticounterfeiting information that is easy to erase.The in situ postsynthesis of the luminescent quick response codes via inkjet printing facilitates precision chemistry control to change the emission ranging from deep-blue(peaking at 407 nm)to orange-red(peaking at 597 nm).The encrypted information can be quickly erased either by modulating the temperature to dissociate the weak coordination or strong Lewis base to promote a neutralization reaction.展开更多
基金the financial support from the National Natural Science Foundation of China(grant nos.22122109 and 22271253,X.H.,U22A20389)the National Key R&D Program of China(grant no.2022YFA1504301,X.H.)+7 种基金the Zhejiang Provincial Natural Science Foundation of China under grant no.LDQ23B020002(X.H.)the Starry Night Science Fund of Zhejiang University Shanghai Institute for Advanced Study(grant no.SN-ZJU-SIAS-006,X.H.)the Beijing National Laboratory for Molecular Sciences(grant no.BNLMS202102,X.H.)the Chinese Academy of Sciences Youth Interdisciplinary Team(grant no.JCTD-2021-11,X.H.)the Fundamental Research Funds for the Central Universities(grant nos.226-2022-00140,226-2022-00224,226-2023-00115,and 226-2024-00003,X.H.)the State Key Laboratory of Clean Energy Utilization(grant no.ZJUCEU2020007,X.H.)the State Key Laboratory of Physical Chemistry of Solid Surfaces(grant no.202210,X.H.)the Leading Innovation Team grant from the Department of Science and Technology of Zhejiang Province(grant no.2022R01005,X.H.).
文摘Cinchoninium has emerged as a powerful scaffold with its distinctive chiral environment and diverse weak bonding interactions.This strategy has successfully enabled a series of highly reactive and selective asymmetric transformations,with umpolung Michael addition of imines being a representative example.However,the understanding of chirality control in these transformations is hindered by the diverse and directionless nature of weak bonding interactions,rendering the stereochemical model elusive.In this study,we present a mechanistic investigation of the stereochemical model and selectivity-controlling factors of the titled reaction.The addition of azaallyl anion to enal is identified as the rate-and selectivity-determining step.In this favorable addition transition state,a new catalyst-substrate binding mode is elucidated:cinchoninium binds the enal oxygen through multiple positively charged C-H bonds in the quinuclidinium core,while the position of azaallyl anion is governed by nonclassical hydrogen-bonding interactions with the peripheral phenyl C-H bonds of the catalyst.A total set of seven weak bonding interactions collectively establish a specific chiral environment that stabilizes only one out of eight possible Michael addition transition states,thus achieving the observed regio-and stereoselectivity.Subsequent titration experiments were conducted to validate the proposed weak bonding network.These mechanistic insights led to the establishment of a quantitative structure-enantioselectivity relationship through a multivariate linear regression approach.Our findings provide a comprehensive stereochemical model for understanding cinchoninium-catalyzed umpolung transformations of imines,elucidating the key functional groups responsible for the chirality control in this catalytic system.The mechanistic insights obtained serve as a rational basis for future designs of related asymmetric transformations.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51771144 and 62104189)the Natural Science Foundation of Shaanxi Province,China(Grant Nos.2021JC-06,2019TD-020,and 2019JLM-30)+1 种基金the China Postdoctoral Science Foundation(Grant No.2020M683483)the Fundamental scientific research business expenses of Xi'an Jiaotong University(Grant No.XZY022020017).
文摘Amorphous indium-gallium-zinc oxide(a-IGZO)thin films are prepared by pulsed laser deposition and fabricated into thin-film transistor(TFT)devices.In-situ x-ray photoelectron spectroscopy(XPS)illustrates that weakly bonded oxygen(O)atoms exist in a-IGZO thin films deposited at high O_(2) pressures,but these can be eliminated by vacuum annealing.The threshold voltage(V_(th))of the a-IGZO TFTs is shifted under positive gate bias,and the Vth shift is positively related to the deposition pressure.A temperature variation experiment in the range of 20 K-300 K demonstrates that an activation energy of 144 meV is required for the Vth shift,which is close to the activation energy required for the migration of weakly bonded O atoms in a-IGZO thin films.Accordingly,the Vth shift is attributed to the acceptor-like states induced by the accumulation of weakly bonded O atoms at the a-IGZO/SiO_(2) interface under positive gate bias.These results provide an insight into the mechanism responsible for the Vth shift of the a-IGZO TFTs and help in the production of reliable designs.
基金supported by the Research Council of Lithuania(LMTLT),agreement no.S-MIP-22-5.
文摘Adhesively bonded joints are widely used in modern lightweight structures due to their high strengthto-weight ratio and design flexibility.However,the reliable non-destructive evaluation of bond integrity remains a significant challenge.This study presents a numerical investigation of adhesively bonded joints with different adhesive properties using ultrasonic guided waves.The main focus of the investigation is to evaluate the feasibility of using guided waves to assess bond integrity,particularly for detecting challenging weak bonds.For this purpose,a theoretical analysis of dispersion curves was conducted,revealing that the S0 Lamb wave mode is significantly sensitive to variations in adhesive properties in the 300-700 kHz frequency range.Finite element modelling was used to analyse the propagation of guided waves in two scenarios:an adhesively bonded aluminum structure and a more complex configuration-adhesively bonded lap joints.The Short-Time Fourier Transform(STFT)was used to process the obtained results and determine the group velocities of guided waves.By analysing the group velocity characteristics,their dependence on the adhesive properties was identified.In the first scenario,a clear separation of S0 modes from A0 modes was observed in the STFT analysis,with a decrease in group velocity as adhesive stiffness increased.For the more complex lap joint scenario,the separation between A0 and S0 modes was less distinct.However,the analysis of the average group velocity shows a dependence of average group velocity on adhesive properties.This is similar to the first scenario.There is a decrease in average group velocity as adhesive stiffness increases.The results obtained demonstrate that guided wavebased methods have a high potential for non-destructive evaluation of adhesively bonded structures,including the detection of weak bonds.
基金Project supported by the Youth Science and Technology Talent Project of Hunan Province of China (Grant No.2022RC1197)the National Natural Science Foundation of China (Grant No.52372260)。
文摘Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials.In this paper,we present a first-principles calculations of the phonon transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers.Both materials possess low lattice thermal conductivity,at least two orders of magnitude lower than graphene and h-BN.The room temperature thermal conductivity of Pb_(2)SbAs(0.91 W/m K)is only a quarter of that of Pb_(2)PAs(3.88 W/m K).We analyze in depth the bonding,lattice dynamics,and phonon mode level information of these materials.Ultimately,it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures.Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb_(2)PAs and Pb_(2)SbAs,and the three-phonon scattering is sufficient to describe their anharmonicity.In this study,the thermal transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers are illuminated based on fundamental physical mechanisms,and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.
基金supported by the National Natural Science Foundation of China(Nos.52034006,52004229,52225401,and 52274231)the Regional Innovation Cooperation Project of Sichuan Province(No.2022YFQ0059)+3 种基金Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(No.2020CX040301)Natural Science Foundation of Sichuan Province(No.2023NSFSC0431)Science and Technology Strategic Cooperation Project between Nanchong City and Southwest Petroleum University(No.SXHZ004)Research and innovation Fund for Graduate Students of Southwest Petroleum University(No.2022KYCX058).
文摘Hydraulic-electric rock fragmentation(HERF)plays a significant role in improving the efficiency of high voltage pulse rock breaking.However,the underlying mechanism of HERF remains unclear.In this study,considering the heterogeneity of the rock,microscopic thermodynamic properties,and shockwave time domain waveforms,based on the shockwave model,digital imaging technology and the discrete element method,the cyclic loading numerical simulations of HERF is achieved by coupling electrical,thermal,and solid mechanics under different formation temperatures,confining pressure,initial peak voltage,electrode bit diameter,and loading times.Meanwhile,the HERF discharge system is conducive to the laboratory experiments with various electrical parameters and the resulting broken pits are numerically reconstructed to obtain the geometric parameters.The results show that,the completely broken area consists of powdery rock debris.In the pre-broken zone,the mineral cementation of the rock determines the transition of type CⅠcracks to type CⅡand type CⅢcracks.Furthermore,the peak pressure of the shockwave increased with initial peak voltage but decreased with electrode bit diameter,while the wave front time reduced.Moreover,increasing well depth,formation temperature and confining pressure augment and inhibit HERF,but once confining pressure surpassed the threshold of 60 MPa for 152.40,215.90,and 228.60 mm electrode bits,and 40 MPa for 309.88 mm electrode bits,HERF is promoted.Additionally,for the same kind of rock,the volume and width of the broken pit increase with higher initial peak voltage and rock fissures will promote HERF.Eventually,the electrode drill bit with a 215.90 mm diameter is more suitable for drilling pink granite.This research contributes to a better microscopic understanding of HERF and provides valuable insights for electrode bit selection,as well as the optimization of circuit parameters for HERF technology.
基金financially supported by the National Natural Science Foundation of China(No.62175189)the Program for Promoting Academic Collaboration and Senior Talent Fostering between China and Canada,Australia,New Zealand,and Latin America(2021-109)the joint China-Sweden Mobility programme(No.52211530052).
文摘Lewis acid−base adducts resulting from instantaneous interactions provide a cost-effective strategy for color tuning and anticounterfeiting information.Herein,we report the construction of luminescent Lewis acid−base adducts via inkjet printing.Due to the unique weak coordination bond of B→N,it is feasible to construct anticounterfeiting information that is easy to erase.The in situ postsynthesis of the luminescent quick response codes via inkjet printing facilitates precision chemistry control to change the emission ranging from deep-blue(peaking at 407 nm)to orange-red(peaking at 597 nm).The encrypted information can be quickly erased either by modulating the temperature to dissociate the weak coordination or strong Lewis base to promote a neutralization reaction.
