The direct synthesis of C2 hydrocarbons （ethylene, acetylene and ethane） from methane is one of the most important task in C1 chemistry. Higher conversion of methane and selectivity to C2 hydrocarbons can be real-iz...The direct synthesis of C2 hydrocarbons （ethylene, acetylene and ethane） from methane is one of the most important task in C1 chemistry. Higher conversion of methane and selectivity to C2 hydrocarbons can be real-ized through plasma reaction. In order to explore the reaction process and mechanism, the possible reaction paths （1）—（4） were proposed on coupling reaction of methane through plasma and studied theoretically using semi-PM3 method [PM3 is parameterization method of modified neglect of diatomic overlap （MNDO）] including determining the transition state, calculating the activation energy and thermodynamic state functions and analyzing the bond or-der and intrinsic reaction coordinate. The reaction heat results indicate that the reactions （2） and （4） are exothermic, while reactions of （1） and （3） are endothermic. The activation energy results show that activation energy for reac-tions （1） and （2） was much lower than that of reaction paths （3） and （4）. Therefore, paths （1） and （2） is the favorable reaction path energetically. More interestingly by comparing the intrinsic reaction coordinated （IRC） of the reaction paths （1） and （2）, it is found that the variations of bond lengths in reaction path （1） has a crucial effect on the poten-tial energy, while in reaction path （2）, the adjustment of the system geometry also contributes to the whole potential energy of the system.展开更多
The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rota...The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rotation technique. When the pump power reaches the mode-locked threshold, the metastable pulse train with a tunable repetition rate is obtained in the transition from the continuous wave state to the passive mode-locked state via proper adjustment of the polarization controller. A simpie model has been established to explain the experimental observation.展开更多
Stone–Wales(SW) defects are possibly formed in graphene and other two-dimensional materials, and have multiple influence on their physical and chemical properties. In this study, the transition state of SW defects in...Stone–Wales(SW) defects are possibly formed in graphene and other two-dimensional materials, and have multiple influence on their physical and chemical properties. In this study, the transition state of SW defects in graphene is determined with the fully discrete Peierls theory. Furthermore, the atomic formation process is investigated by means of ab-initio simulations. The atomic structure change and energetics of the SW transformation are revealed. It is found that the transition state is at the SW bond rotation of 34.5°and the activation energy barrier is about 12 eV. This work provides a new method to investigate SW transformations in graphene-like materials and to explore unknown SW-type defects in other 2D materials.展开更多
Theoretical studies on the rearrangement reactions of nitropyrazoles have beeninvestigated. In order to gain a better understanding of the intermediate process of rearrangementreactions, the transition states of the r...Theoretical studies on the rearrangement reactions of nitropyrazoles have beeninvestigated. In order to gain a better understanding of the intermediate process of rearrangementreactions, the transition states of the rearrangement reactions were obtained by TS method at theB3LYP/6-311G（d, p） level of theory. The natural bond orbital charge, electrostatic potential andfrontier molecular orbital of the molecules in the process of rearrangement were analyzed, and thesolvent effect was also discussed. The rearrangement of nitropyrazoles involves two transitionstates and one intermediate, and the nitro group and hydrogen atom are two transfer groups forrearrangement reactions. The migration of these two groups leads to the change of chargedistribution and molecular structure. The structural changes of the molecules in different solventsare not significant, but the dipole moment of the molecule has obvious change.展开更多
The presence of a solvent interacting with a system brings about qualitative changes from the corresponding gas-phase reactions. A solvent can not only change the energetics along the reaction pathway, but also radica...The presence of a solvent interacting with a system brings about qualitative changes from the corresponding gas-phase reactions. A solvent can not only change the energetics along the reaction pathway, but also radically alter the reaction mechanism. Here, we investigated the water-induced transition state of the OH^-＋CO2→HCO3^- reaction using a multi-level quantum mechanics and molecular mechanics method with an explicit water model. The solvent energy contribution along the reaction pathway has a maximum value which induces the highest energy point on the potential of mean force. The charge transfer from OH^- to CO2 results in the breaking of the OH^- solvation shell and the forming of the CO2 solvation shell. The loss of hydrogen bonds in the OH^- solvation shell without being compensated by the formation of hydrogen bonds in the CO2 solvation shell induces the transition state in the aqueous solution. The calculated free energy reaction barrier at the CCSD（T）/MM level of theory, 11.8 kcal/mol, agrees very well with the experimental value, 12.1 kcal/mol.展开更多
The study on transition states is one of the most important pathways to understand the essence of chemical reactions. With the development of femtoseeond pulse technique, Zewail et al. have carried out a number of exp...The study on transition states is one of the most important pathways to understand the essence of chemical reactions. With the development of femtoseeond pulse technique, Zewail et al. have carried out a number of experimental studies on the transition states, while the theoretical chemists has a great interest in the topic. In the previous展开更多
Elexible variety has all along been a hallmark of America’s global strategy withdifferentiated treatment for specific nations. In the new century, Washingtondivides the major world forces into four categories in ligh...Elexible variety has all along been a hallmark of America’s global strategy withdifferentiated treatment for specific nations. In the new century, Washingtondivides the major world forces into four categories in light of a comprehensive crite-rion of whether they have been fused into the international system, are going to-ward democracy or benefit world stability. They include: insiders or allies (Europeand Japan), marginalized ones (some underdeveloped African nations), outsidersor "rogues" (Iraq, North Korea) and finally, travelers on the way or "transitionstates". Interpretations by U.S. strategic reports define the "transition states"展开更多
In this paper, numerical simulation of shock-induced chemical reactions of intermetallic mixtures is discussed. Specifically, the paper focuses on intermetallic mixture of nickel and aluminum. To initiate the chemical...In this paper, numerical simulation of shock-induced chemical reactions of intermetallic mixtures is discussed. Specifically, the paper focuses on intermetallic mixture of nickel and aluminum. To initiate the chemical reactions, the thermal input or the shockwave should supply the energy to take the reactants, mixture of nickel and aluminum, to the transition state. Thus, for any numerical simulation or analysis of the shock or thermally induced chemical reaction in a continuum scale or a meso scale, it is necessary to identify the transition state. The transition state for the intermetallic mixture of nickel and the aluminum is identified in this paper and a result of the numerical simulation of the shock-induced chemical reaction, in a continuum scale is presented. The numerical solutions clearly show the chemical reactions, release of heat energy, increase of the temperature and the formation of products, following the transition state and the resulting shock-induced chemical reaction of a binary intermetallic energetic mixture of nickel and aluminum. The studies also show that the collapse of porosity is a mechanism that takes the reactants to the transition state, in shock-induced chemical reactions of binary intermetallic mixtures.展开更多
TiO_(2) cluster sensitivity to acetone adsorption using transition state theory is investigated.Ti_(10)O_(20) cluster is used to perform the calculations using density functional theory with dispersion corrections.Ads...TiO_(2) cluster sensitivity to acetone adsorption using transition state theory is investigated.Ti_(10)O_(20) cluster is used to perform the calculations using density functional theory with dispersion corrections.Adsorption state and transition state are calculated via thermodynamic energies,i.e.,Gibbs free energy of adsorption and activation.Reaction rate,response,response time,and recovery time as a function of temperature and acetone concentration are calculated.Acetone burning in the air due to autoignition is considered using a logistic function.The results of the theory are compared with available experimental findings that revealed the quality of both theoretical and experimental results.The response time decreases with respect to acetone concentration.On the other hand,the recovery time in the desorption phase increases with acetone concentration.The temperature of maximum response is 356℃,while the maximum response value is 2.9.展开更多
The response of steady-state fluorescence (Fs) to irradiance in apple (Malus pumila Mill. cv. Tengmu No.1/Malus hupehensis Rehd.) leaf increased and decreased at light levels below and above 400 mumol(.)m(-2.)s(-1) ph...The response of steady-state fluorescence (Fs) to irradiance in apple (Malus pumila Mill. cv. Tengmu No.1/Malus hupehensis Rehd.) leaf increased and decreased at light levels below and above 400 mumol(.)m(-2.)s(-1) photosynthetic photon flux density (PPFD), respectively, while the light-adapted maximal fluorescence (Fm') and minimal fluorescence (Fo') decreased constantly with the increasing PPFD, and the closure of photosystem 11 reaction center (PS 11 RC) increased continuously, reflected by the chlorophyll fluorescence parameter of (Fs-Fo')/(Fm'-Fo'). These facts indicated that decrease of Fs above 400 mumol(.)m(-2.)s(-1) PPFD was not caused by closure of PS 11 RC, but was mainly resulted from the process of light transfer from light-harvesting complex II (LHC II) to PS II RC. In the presence of N- ethylmaleimide (NEM), an inhibitor of photosynthetic state transition, Fs kept on increasing in apple leaf at light levels from 400 to 700 mumol(.)m(-1.)s(-1), which was the photosynthetic saturation irradiance of apple leaves. In addition, Fs still increased at light levels over 700 mumol(.)m(-2.)s(-1) in apple leaf pre-treated with dithiothreitol (DTT), an inhibitor of xanthophyll cycle. These changes showed that state transition and xanthophyll cycle caused a decrease of Fs in apple leaf at light levels below and above the photosynthetic saturation irradiance, respectively. When apple leaf was pre-treated with NEM, the PS II apparent rate of photochemical reaction (P-rate) and photochemical quenching (qP) decreased significantly in the light range of 600-800 mumol(.)m(-2.)s(-1), but the non-photochemical quenching (qN) existed a small increase at 600-800 mumol(.)m(-2.)s(-1) and a decrease above 800 mumol(.)m(-2.)s(-1). These phenomena suggested that state transition was mainly a photochemical and a non-photochemical process in apple leaf responding to light lower and higher than photosynthetic saturation irradiance, respectively.展开更多
The two possible reaction paths of producing ethane on coupling reaction of methane through plasma were theoretically investigated by B3LYP and MP2 methods with 6-311G* respectively and further compared with the previ...The two possible reaction paths of producing ethane on coupling reaction of methane through plasma were theoretically investigated by B3LYP and MP2 methods with 6-311G* respectively and further compared with the previous results calculated from B3LYP/6-31G*. The new investigated results consistently confirmed the previous conclusion. And the influences of the calculation methods and basis sets on the calculated results were also dis-cussed.展开更多
The reaction of disilane with atomic hydrogen has been studied. This reaction involves both substitution and abstraction. Calculations show that the hydrogen abstraction is the strongest competing channel. The canonic...The reaction of disilane with atomic hydrogen has been studied. This reaction involves both substitution and abstraction. Calculations show that the hydrogen abstraction is the strongest competing channel. The canonical variational transition state theory with a small curvature tunneling correction (SCT) has been used for the kinetic calculation. The theoretical results are in good agreement with the available experimental data. Comparing the reactions of atomic hydrogen with disilane and silane, it can be seen that the reactivity of the Si-H bond is higher in Si2H6than that in SiH4.展开更多
1 Results Sub-and super-critical water is an attractive reaction medium for organic transformation because of their unique properties such as low viscosity,high density,low polarity,high solubility to organic compound...1 Results Sub-and super-critical water is an attractive reaction medium for organic transformation because of their unique properties such as low viscosity,high density,low polarity,high solubility to organic compounds,and,of course,the greenness of the medium[1-3]. We report herein some unique reactions of unsaturated compounds in sub-and super-critical water.When allylbenzene was treated in supercritical water (SCW: 380 ℃,10 min,water density=0.35 g/mL),double bond migrated to give a mixture of allylb...展开更多
In this paper. the abstraction reaction of CH_3SiH_3 with H has been studied by using the 'direct dynamics' method of variational transition-state theory. which is based on the information on geometries. frequ...In this paper. the abstraction reaction of CH_3SiH_3 with H has been studied by using the 'direct dynamics' method of variational transition-state theory. which is based on the information on geometries. frequencies and energies calculalcd by ab inito along the minimum energy path. The rate constants of the title reaction were calculated for the range of temperature 298-1700 K. The rate constants calculated match well with the experimental values.展开更多
Variational transition state theory is used to study the kinetics of the reactions Li+HF and Li+HCl on the BO potential energy surfaces, fitted to ab initio values by Lagana et al. The saddle point, the location of ge...Variational transition state theory is used to study the kinetics of the reactions Li+HF and Li+HCl on the BO potential energy surfaces, fitted to ab initio values by Lagana et al. The saddle point, the location of generalized transition state and other kinetic features on the bottleneck of the po- tential energy surface are obtained. We point out that the location of generalized transition state tends to the direction in which the two atoms with larger reduced mass separate off. It can be determined whether a potential energy surface is accurate or not by a fine analysis of its bottleneck region and a comparison of kinetic calculation with experimental result. This is helpful for building a more accurate potential energy surface.展开更多
In this study, the initial perturbations that are the easiest to trigger the Kuroshio Extension （KE） transition connecting a basic weak jet state and a strong, fairly stable meandering state, are investigated using ...In this study, the initial perturbations that are the easiest to trigger the Kuroshio Extension （KE） transition connecting a basic weak jet state and a strong, fairly stable meandering state, are investigated using a reduced-gravity shallow water ocean model and the CNOP （Conditional Nonlinear Optimal Perturbation） approach. This kind of initial perturbation is called an optimal precursor （OPR）. The spatial structures and evolutionary processes of the OPRs are analyzed in detail. The results show that most of the OPRs are in the form of negative sea surface height （SSH） anomalies mainly located in a narrow band region south of the KE jet, in basic agreement with altimetric observations. These negative SSH anomalies reduce the merid- ional SSH gradient within the KE, thus weakening the strength of the jet. The KE jet then becomes more convoluted, with a high-frequency and large-amplitude variability corresponding to a high eddy kinetic energy level; this gradually strengthens the KE jet through an inverse energy cascade. Eventually, the KE reaches a high-energy state characterized by two well defined and fairly stable anticyclonic meanders. Moreover, sensitivity experiments indicate that the spatial structures of the OPRs are not sensitive to the model parameters and to the optimization times used in the analysis.展开更多
Identifying state transition and determining the critical value of the Duffing oscillator are crucial to indicating external signal existence and have a great influence on detection accuracy in weak signal detection. ...Identifying state transition and determining the critical value of the Duffing oscillator are crucial to indicating external signal existence and have a great influence on detection accuracy in weak signal detection. A circular zone counting （CZC） method is proposed in this paper, by combining the Duffing oscillator＇s phase trajectory feature and numerical calculation for quickly and accurately identifying state transition and determining the critical value, to realize a high- efficiency weak signal detection. Detailed model analysis and method construction of the CZC method are introduced. Numerical experiments into the reliability of the proposed CZC method compared with the maximum Lyapunov exponent （MLE） method are carried out. The CZC method is demonstrated to have better detecting ability than the MLE method, and furthermore it is simpler and clearer in calculation to extend to engineering application.展开更多
We have precisely derived a ＂rigorous instantaneous formulation＂ for transitions between two bound states when the bound states are well-described by instantaneous Bethe-Salpeter （BS） equation （i.e. the kernel of...We have precisely derived a ＂rigorous instantaneous formulation＂ for transitions between two bound states when the bound states are well-described by instantaneous Bethe-Salpeter （BS） equation （i.e. the kernel of the equation is instantaneous ＂occasionally＂）. The obtained rigorous instantaneous formulation, in fact, is expressed as an operator sandwiched by two ＂reduced BS wave functions＂ properly, while the reduced BS wave functions appearing in the formulation are the rigorous solutions of the instantaneous BS equation, and they may relate to Schroedinger wave functions straightforwardly. We also show that the rigorous instantaneous formulation is gauge-invariant with respect to the Uem（1） transformation precisely, if the concerned transitions are radiative. Some applications of the formulation are outlined.展开更多
ATP-binding cassette exporters transport many substrates out of cellular membranes via alternating between inward-facing and outward-facing conformations. Despite extensive research efforts over the past decades, unde...ATP-binding cassette exporters transport many substrates out of cellular membranes via alternating between inward-facing and outward-facing conformations. Despite extensive research efforts over the past decades, understanding of the molecular mechanism remains elusive. As these large-scale conformational movements are global and collective, we have previously performed extensive coarse-grained molecular dynamics simulations of the potential of mean force along the conformational transition pathway [J. Phys. Chem. B 119, 1295(2015)]. However, the occluded conformational state, in which both the internal and external gate are closed, was not determined in the calculated free energy profile. In this work, we extend the above methods to the calculation of the free energy profile along the reaction coordinate, d1-d2, which are the COM distances between the two sides of the internal(d1)and the external gate(d2). The potential of mean force is thus obtained to identify the transition pathway, along which several outward-facing, inward-facing, and occluded state structures are predicted in good agreement with structural experiments. Our coarse-grained molecular dynamics free-energy simulations demonstrate that the internal gate is closed before the external gate is open during the inward-facing to outward-facing transition and vice versa during the inward-facing to outward-facing transition. Our results capture the unidirectional feature of substrate translocation via the exporter, which is functionally important in biology. This finding is different from the previous result, in which both the internal and external gates are open reported in an X-ray experiment [Proc. Natl. Acad. Sci. USA 104,19005(2007)]. Our study sheds light on the molecular mechanism of the state transitions in an ATP-binding cassette exporter.展开更多
The structural features and three-dimensional nature of the charge density wave （CDW） state of the layered chalcogenide 1T-TaSe2-xTex （0≤x≤2.0） are characterized by Cs-corrected transmission electron microscopy ...The structural features and three-dimensional nature of the charge density wave （CDW） state of the layered chalcogenide 1T-TaSe2-xTex （0≤x≤2.0） are characterized by Cs-corrected transmission electron microscopy measurements. Notable changes of both average structure and the CDW state arising from Te substitution for Se are clearly demonstrated in samples with x〉0.3. The commensurate CDW state characterized by the known star-of-David clustering in the 1T-TaSe2 crystal becomes visibly unstable with Te substitution and vanishes when x=0.3. The 1T-TaSe2-xTex （0.3≤x≤1.3） samples generally adopt a remarkable incommensurate CDW state with monoclinic distortion, which could be fundamentally in correlation with the strong qq-dependent electron-phonon coupling-induced period-lattice-distortion as identified in TaTe22. Systematic analysis demonstrates that the occurrence of superconductivity is related to the suppression of the commensurate CDW phase and the presence of discommensuration is an evident structural feature observed in the superconducting samples.展开更多
基金Supported by the National Natural Science Foundation of China (No.20606023).
文摘The direct synthesis of C2 hydrocarbons （ethylene, acetylene and ethane） from methane is one of the most important task in C1 chemistry. Higher conversion of methane and selectivity to C2 hydrocarbons can be real-ized through plasma reaction. In order to explore the reaction process and mechanism, the possible reaction paths （1）—（4） were proposed on coupling reaction of methane through plasma and studied theoretically using semi-PM3 method [PM3 is parameterization method of modified neglect of diatomic overlap （MNDO）] including determining the transition state, calculating the activation energy and thermodynamic state functions and analyzing the bond or-der and intrinsic reaction coordinate. The reaction heat results indicate that the reactions （2） and （4） are exothermic, while reactions of （1） and （3） are endothermic. The activation energy results show that activation energy for reac-tions （1） and （2） was much lower than that of reaction paths （3） and （4）. Therefore, paths （1） and （2） is the favorable reaction path energetically. More interestingly by comparing the intrinsic reaction coordinated （IRC） of the reaction paths （1） and （2）, it is found that the variations of bond lengths in reaction path （1） has a crucial effect on the poten-tial energy, while in reaction path （2）, the adjustment of the system geometry also contributes to the whole potential energy of the system.
基金Project supported by the National Natural Science Foundation of China(Grant No.11074078)the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.20094407110002)+1 种基金the Key Program for Scientific and Technological Innovations of Higher Education Institutes in Guangdong Province,China(Grant No.cxzd1011)the Foundation for Distinguished Young Talents in Higher Education of Guangdong,China(Grant No.C10183)
文摘The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rotation technique. When the pump power reaches the mode-locked threshold, the metastable pulse train with a tunable repetition rate is obtained in the transition from the continuous wave state to the passive mode-locked state via proper adjustment of the polarization controller. A simpie model has been established to explain the experimental observation.
基金Project supported by the National Natural Science Foundation of China (Grant No. 11847089)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No. 20KJB430002)GuiZhou Provincial Department of Science and Technology, China (Grant No. QKHJC[2019]1167)。
文摘Stone–Wales(SW) defects are possibly formed in graphene and other two-dimensional materials, and have multiple influence on their physical and chemical properties. In this study, the transition state of SW defects in graphene is determined with the fully discrete Peierls theory. Furthermore, the atomic formation process is investigated by means of ab-initio simulations. The atomic structure change and energetics of the SW transformation are revealed. It is found that the transition state is at the SW bond rotation of 34.5°and the activation energy barrier is about 12 eV. This work provides a new method to investigate SW transformations in graphene-like materials and to explore unknown SW-type defects in other 2D materials.
文摘Theoretical studies on the rearrangement reactions of nitropyrazoles have beeninvestigated. In order to gain a better understanding of the intermediate process of rearrangementreactions, the transition states of the rearrangement reactions were obtained by TS method at theB3LYP/6-311G（d, p） level of theory. The natural bond orbital charge, electrostatic potential andfrontier molecular orbital of the molecules in the process of rearrangement were analyzed, and thesolvent effect was also discussed. The rearrangement of nitropyrazoles involves two transitionstates and one intermediate, and the nitro group and hydrogen atom are two transfer groups forrearrangement reactions. The migration of these two groups leads to the change of chargedistribution and molecular structure. The structural changes of the molecules in different solventsare not significant, but the dipole moment of the molecule has obvious change.
基金supported by the National Natural Science Foundation of China(Grant No.11374194)Taishan Scholarship Fund from Shandong Province,China
文摘The presence of a solvent interacting with a system brings about qualitative changes from the corresponding gas-phase reactions. A solvent can not only change the energetics along the reaction pathway, but also radically alter the reaction mechanism. Here, we investigated the water-induced transition state of the OH^-＋CO2→HCO3^- reaction using a multi-level quantum mechanics and molecular mechanics method with an explicit water model. The solvent energy contribution along the reaction pathway has a maximum value which induces the highest energy point on the potential of mean force. The charge transfer from OH^- to CO2 results in the breaking of the OH^- solvation shell and the forming of the CO2 solvation shell. The loss of hydrogen bonds in the OH^- solvation shell without being compensated by the formation of hydrogen bonds in the CO2 solvation shell induces the transition state in the aqueous solution. The calculated free energy reaction barrier at the CCSD（T）/MM level of theory, 11.8 kcal/mol, agrees very well with the experimental value, 12.1 kcal/mol.
基金Supported by the National Natural Science Foundation of China
文摘The study on transition states is one of the most important pathways to understand the essence of chemical reactions. With the development of femtoseeond pulse technique, Zewail et al. have carried out a number of experimental studies on the transition states, while the theoretical chemists has a great interest in the topic. In the previous
文摘Elexible variety has all along been a hallmark of America’s global strategy withdifferentiated treatment for specific nations. In the new century, Washingtondivides the major world forces into four categories in light of a comprehensive crite-rion of whether they have been fused into the international system, are going to-ward democracy or benefit world stability. They include: insiders or allies (Europeand Japan), marginalized ones (some underdeveloped African nations), outsidersor "rogues" (Iraq, North Korea) and finally, travelers on the way or "transitionstates". Interpretations by U.S. strategic reports define the "transition states"
文摘In this paper, numerical simulation of shock-induced chemical reactions of intermetallic mixtures is discussed. Specifically, the paper focuses on intermetallic mixture of nickel and aluminum. To initiate the chemical reactions, the thermal input or the shockwave should supply the energy to take the reactants, mixture of nickel and aluminum, to the transition state. Thus, for any numerical simulation or analysis of the shock or thermally induced chemical reaction in a continuum scale or a meso scale, it is necessary to identify the transition state. The transition state for the intermetallic mixture of nickel and the aluminum is identified in this paper and a result of the numerical simulation of the shock-induced chemical reaction, in a continuum scale is presented. The numerical solutions clearly show the chemical reactions, release of heat energy, increase of the temperature and the formation of products, following the transition state and the resulting shock-induced chemical reaction of a binary intermetallic energetic mixture of nickel and aluminum. The studies also show that the collapse of porosity is a mechanism that takes the reactants to the transition state, in shock-induced chemical reactions of binary intermetallic mixtures.
文摘TiO_(2) cluster sensitivity to acetone adsorption using transition state theory is investigated.Ti_(10)O_(20) cluster is used to perform the calculations using density functional theory with dispersion corrections.Adsorption state and transition state are calculated via thermodynamic energies,i.e.,Gibbs free energy of adsorption and activation.Reaction rate,response,response time,and recovery time as a function of temperature and acetone concentration are calculated.Acetone burning in the air due to autoignition is considered using a logistic function.The results of the theory are compared with available experimental findings that revealed the quality of both theoretical and experimental results.The response time decreases with respect to acetone concentration.On the other hand,the recovery time in the desorption phase increases with acetone concentration.The temperature of maximum response is 356℃,while the maximum response value is 2.9.
文摘The response of steady-state fluorescence (Fs) to irradiance in apple (Malus pumila Mill. cv. Tengmu No.1/Malus hupehensis Rehd.) leaf increased and decreased at light levels below and above 400 mumol(.)m(-2.)s(-1) photosynthetic photon flux density (PPFD), respectively, while the light-adapted maximal fluorescence (Fm') and minimal fluorescence (Fo') decreased constantly with the increasing PPFD, and the closure of photosystem 11 reaction center (PS 11 RC) increased continuously, reflected by the chlorophyll fluorescence parameter of (Fs-Fo')/(Fm'-Fo'). These facts indicated that decrease of Fs above 400 mumol(.)m(-2.)s(-1) PPFD was not caused by closure of PS 11 RC, but was mainly resulted from the process of light transfer from light-harvesting complex II (LHC II) to PS II RC. In the presence of N- ethylmaleimide (NEM), an inhibitor of photosynthetic state transition, Fs kept on increasing in apple leaf at light levels from 400 to 700 mumol(.)m(-1.)s(-1), which was the photosynthetic saturation irradiance of apple leaves. In addition, Fs still increased at light levels over 700 mumol(.)m(-2.)s(-1) in apple leaf pre-treated with dithiothreitol (DTT), an inhibitor of xanthophyll cycle. These changes showed that state transition and xanthophyll cycle caused a decrease of Fs in apple leaf at light levels below and above the photosynthetic saturation irradiance, respectively. When apple leaf was pre-treated with NEM, the PS II apparent rate of photochemical reaction (P-rate) and photochemical quenching (qP) decreased significantly in the light range of 600-800 mumol(.)m(-2.)s(-1), but the non-photochemical quenching (qN) existed a small increase at 600-800 mumol(.)m(-2.)s(-1) and a decrease above 800 mumol(.)m(-2.)s(-1). These phenomena suggested that state transition was mainly a photochemical and a non-photochemical process in apple leaf responding to light lower and higher than photosynthetic saturation irradiance, respectively.
基金Project supported by the Natural Science Foundation of Tianjin Education Commission (No. 20020902) and the Youth Fund Project of Tianjin Nor-mal University (No. 52LE31).
文摘The two possible reaction paths of producing ethane on coupling reaction of methane through plasma were theoretically investigated by B3LYP and MP2 methods with 6-311G* respectively and further compared with the previous results calculated from B3LYP/6-31G*. The new investigated results consistently confirmed the previous conclusion. And the influences of the calculation methods and basis sets on the calculated results were also dis-cussed.
基金the Research Fund for the Doctoral Program of High Education of China (Grant No. 1999042201).
文摘The reaction of disilane with atomic hydrogen has been studied. This reaction involves both substitution and abstraction. Calculations show that the hydrogen abstraction is the strongest competing channel. The canonical variational transition state theory with a small curvature tunneling correction (SCT) has been used for the kinetic calculation. The theoretical results are in good agreement with the available experimental data. Comparing the reactions of atomic hydrogen with disilane and silane, it can be seen that the reactivity of the Si-H bond is higher in Si2H6than that in SiH4.
文摘1 Results Sub-and super-critical water is an attractive reaction medium for organic transformation because of their unique properties such as low viscosity,high density,low polarity,high solubility to organic compounds,and,of course,the greenness of the medium[1-3]. We report herein some unique reactions of unsaturated compounds in sub-and super-critical water.When allylbenzene was treated in supercritical water (SCW: 380 ℃,10 min,water density=0.35 g/mL),double bond migrated to give a mixture of allylb...
文摘In this paper. the abstraction reaction of CH_3SiH_3 with H has been studied by using the 'direct dynamics' method of variational transition-state theory. which is based on the information on geometries. frequencies and energies calculalcd by ab inito along the minimum energy path. The rate constants of the title reaction were calculated for the range of temperature 298-1700 K. The rate constants calculated match well with the experimental values.
基金Project supported by the National Natural Science Foundation of China.
文摘Variational transition state theory is used to study the kinetics of the reactions Li+HF and Li+HCl on the BO potential energy surfaces, fitted to ab initio values by Lagana et al. The saddle point, the location of generalized transition state and other kinetic features on the bottleneck of the po- tential energy surface are obtained. We point out that the location of generalized transition state tends to the direction in which the two atoms with larger reduced mass separate off. It can be determined whether a potential energy surface is accurate or not by a fine analysis of its bottleneck region and a comparison of kinetic calculation with experimental result. This is helpful for building a more accurate potential energy surface.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41576015, 41306023, 41490644 and 41490640)the Natural Science Foundation Of China (NSFC) Innovative Group (Grant No. 41421005)+1 种基金the NSFC–Shandong Joint Fund for Marine Science Research Centers (Grant No. U1406401)support from the University of Naples Parthenope (Grant No. DSTE315)
文摘In this study, the initial perturbations that are the easiest to trigger the Kuroshio Extension （KE） transition connecting a basic weak jet state and a strong, fairly stable meandering state, are investigated using a reduced-gravity shallow water ocean model and the CNOP （Conditional Nonlinear Optimal Perturbation） approach. This kind of initial perturbation is called an optimal precursor （OPR）. The spatial structures and evolutionary processes of the OPRs are analyzed in detail. The results show that most of the OPRs are in the form of negative sea surface height （SSH） anomalies mainly located in a narrow band region south of the KE jet, in basic agreement with altimetric observations. These negative SSH anomalies reduce the merid- ional SSH gradient within the KE, thus weakening the strength of the jet. The KE jet then becomes more convoluted, with a high-frequency and large-amplitude variability corresponding to a high eddy kinetic energy level; this gradually strengthens the KE jet through an inverse energy cascade. Eventually, the KE reaches a high-energy state characterized by two well defined and fairly stable anticyclonic meanders. Moreover, sensitivity experiments indicate that the spatial structures of the OPRs are not sensitive to the model parameters and to the optimization times used in the analysis.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61172047 and 61071025)
文摘Identifying state transition and determining the critical value of the Duffing oscillator are crucial to indicating external signal existence and have a great influence on detection accuracy in weak signal detection. A circular zone counting （CZC） method is proposed in this paper, by combining the Duffing oscillator＇s phase trajectory feature and numerical calculation for quickly and accurately identifying state transition and determining the critical value, to realize a high- efficiency weak signal detection. Detailed model analysis and method construction of the CZC method are introduced. Numerical experiments into the reliability of the proposed CZC method compared with the maximum Lyapunov exponent （MLE） method are carried out. The CZC method is demonstrated to have better detecting ability than the MLE method, and furthermore it is simpler and clearer in calculation to extend to engineering application.
基金The project supported in part by National Natural Science Foundation of China
文摘We have precisely derived a ＂rigorous instantaneous formulation＂ for transitions between two bound states when the bound states are well-described by instantaneous Bethe-Salpeter （BS） equation （i.e. the kernel of the equation is instantaneous ＂occasionally＂）. The obtained rigorous instantaneous formulation, in fact, is expressed as an operator sandwiched by two ＂reduced BS wave functions＂ properly, while the reduced BS wave functions appearing in the formulation are the rigorous solutions of the instantaneous BS equation, and they may relate to Schroedinger wave functions straightforwardly. We also show that the rigorous instantaneous formulation is gauge-invariant with respect to the Uem（1） transformation precisely, if the concerned transitions are radiative. Some applications of the formulation are outlined.
基金supported by the National Natu-ral Science Foundation of China(No.21073170 and No.21273209).
文摘ATP-binding cassette exporters transport many substrates out of cellular membranes via alternating between inward-facing and outward-facing conformations. Despite extensive research efforts over the past decades, understanding of the molecular mechanism remains elusive. As these large-scale conformational movements are global and collective, we have previously performed extensive coarse-grained molecular dynamics simulations of the potential of mean force along the conformational transition pathway [J. Phys. Chem. B 119, 1295(2015)]. However, the occluded conformational state, in which both the internal and external gate are closed, was not determined in the calculated free energy profile. In this work, we extend the above methods to the calculation of the free energy profile along the reaction coordinate, d1-d2, which are the COM distances between the two sides of the internal(d1)and the external gate(d2). The potential of mean force is thus obtained to identify the transition pathway, along which several outward-facing, inward-facing, and occluded state structures are predicted in good agreement with structural experiments. Our coarse-grained molecular dynamics free-energy simulations demonstrate that the internal gate is closed before the external gate is open during the inward-facing to outward-facing transition and vice versa during the inward-facing to outward-facing transition. Our results capture the unidirectional feature of substrate translocation via the exporter, which is functionally important in biology. This finding is different from the previous result, in which both the internal and external gates are open reported in an X-ray experiment [Proc. Natl. Acad. Sci. USA 104,19005(2007)]. Our study sheds light on the molecular mechanism of the state transitions in an ATP-binding cassette exporter.
基金Supported by the National Basic Research Program of China under Grant Nos 2015CB921300 and 2012CB821404the National Key Research and Development Program of China under Grant Nos 2016YFA0300300 and 2016YFA0300404+1 种基金the National Natural Science Foundation of China under Grant Nos 11474323,11604372,11274368,91221102,11190022,11674326 and 91422303the Strategic Priority Research Program(B)of the Chinese Academy of Sciences under Grant No XDB07020000
文摘The structural features and three-dimensional nature of the charge density wave （CDW） state of the layered chalcogenide 1T-TaSe2-xTex （0≤x≤2.0） are characterized by Cs-corrected transmission electron microscopy measurements. Notable changes of both average structure and the CDW state arising from Te substitution for Se are clearly demonstrated in samples with x〉0.3. The commensurate CDW state characterized by the known star-of-David clustering in the 1T-TaSe2 crystal becomes visibly unstable with Te substitution and vanishes when x=0.3. The 1T-TaSe2-xTex （0.3≤x≤1.3） samples generally adopt a remarkable incommensurate CDW state with monoclinic distortion, which could be fundamentally in correlation with the strong qq-dependent electron-phonon coupling-induced period-lattice-distortion as identified in TaTe22. Systematic analysis demonstrates that the occurrence of superconductivity is related to the suppression of the commensurate CDW phase and the presence of discommensuration is an evident structural feature observed in the superconducting samples.
