The human serotonin transporter(SERT)terminates neurotransmission by removing serotonin from the synaptic cleft,which is an essential process that plays an important role in depression.In addition to natural substrate...The human serotonin transporter(SERT)terminates neurotransmission by removing serotonin from the synaptic cleft,which is an essential process that plays an important role in depression.In addition to natural substrate serotonin,SERT is also the target of the abused drug cocaine and,clinically used antidepressants,escitalopram,and paroxetine.To date,few studies have attempted to investigate the unbinding mechanism underlying the orthosteric and allosteric modulation of SERT.In this article,the conserved property of the orthosteric and allosteric sites(S1 and S2)of SERT was revealed by combining the high resolutions of x-ray crystal structures and molecular dynamics(MD)simulations.The residues Tyr95 and Ser438 located within the S1 site,and Arg104 located within the S2 site in SERT illustrate conserved interactions(hydrogen bonds and hydrophobic interactions),as responses to selective serotonin reuptake inhibitors.Van der Waals interactions were keys to designing effective drugs inhibiting SERT and further,electrostatic interactions highlighted escitalopram as a potent antidepressant.We found that cocaine,escitalopram,and paroxetine,whether the S1 site or the S2 site,were more competitive.According to this potential of mean force(PMF)simulations,the new insights reveal the principles of competitive inhibitors that lengths of trails from central SERT to an opening were~18A for serotonin and~22 A for the above-mentioned three drugs.Furthermore,the distance between the natural substrate serotonin and cocaine(or escitalopram)at the allosteric site was~3A.Thus,it can be inferred that the potent antidepressants tended to bind at deeper positions of the S1 or the S2 site of SERT in comparison to the substrate.Continuing exploring the processes of unbinding four ligands against the two target pockets of SERT,this study observed a broad pathway in which serotonin,cocaine,escitalopram(at the S1 site),and paroxetine all were pulled out to an opening between MT1b and MT6a,which may be helpful to understand the dissociation mechanism of antidepressants.展开更多
In the context of deep rock engineering,the in-situ stress state is of major importance as it plays an important role in rock dynamic response behavior.Thus,stress initialization becomes crucial and is the first step ...In the context of deep rock engineering,the in-situ stress state is of major importance as it plays an important role in rock dynamic response behavior.Thus,stress initialization becomes crucial and is the first step for the dynamic response simulation of rock mass in a high in-situ stress field.In this paper,stress initialization methods,including their principles and operating procedures for reproducing steady in-situ stress state in LS-DYNA,are first introduced.Then the most popular four methods,i.e.,explicit dynamic relaxation(DR)method,implicit-explicit sequence method,Dynain file method and quasi-static method,are exemplified through a case analysis by using the RHT and plastic hardening rock material models to simulate rock blasting under in-situ stress condition.Based on the simulations,it is concluded that the stress initialization results obtained by implicit-explicit sequence method and dynain file method are closely related to the rock material model,and the explicit DR method has an obvious advantage in solution time when compared to other methods.Besides that,it is recommended to adopt two separate analyses for the whole numerical simulation of rock mass under the combined action of in-situ stress and dynamic disturbance.展开更多
The structure and properties of molten salt solution o J Li,K|F,Cl system have been investiged by computerized simulation of molecular dynamic method.The partial RDF,the partial molar energy of mixing and the diffusio...The structure and properties of molten salt solution o J Li,K|F,Cl system have been investiged by computerized simulation of molecular dynamic method.The partial RDF,the partial molar energy of mixing and the diffusion coeffients of Li^+,K^+,F^- and Cl^- have been calculated. The results are in agreement with the experimental values.The regularities of the distribution of ions and mieroscopic holes are discussed based on the results of computerized simulation.展开更多
The computational methods of a typical dynamic mathematical model that can describe the differential element and the inertial element for the system simulation are researched. The stability of numerical solutions of t...The computational methods of a typical dynamic mathematical model that can describe the differential element and the inertial element for the system simulation are researched. The stability of numerical solutions of the dynamic mathematical model is researched. By means of theoretical analysis, the error formulas, the error sign criteria and the error relationship criterion of the implicit Euler method and the trapezoidal method are given, the dynamic factor affecting the computational accuracy has been found, the formula and the methods of computing the dynamic factor are given. The computational accuracy of the dynamic mathematical model like this can be improved by use of the dynamic factor.展开更多
The voltage stability is substantially a dynamic stability, but the primary method which is more mature and engineering practical to analyze the stability of voltage is still static analysis. The time-domain simulatio...The voltage stability is substantially a dynamic stability, but the primary method which is more mature and engineering practical to analyze the stability of voltage is still static analysis. The time-domain simulation is an important measure in research of complex power grid. With the development of full dynamic simulation technology, the research of dynamic voltage stability by using full dynamic simulation program which is based on time-domain simulation can be carried out. This paper uses full dynamic simulation program in dynamic voltage stability research, lays special stress on research in how generator over-excitation limiter functioned and influence in dynamic voltage stability research, and raise 2 methods and steps to figure out dynamic stable voltage in both over-excitation counted and not counted. The simulation results of examples indicate the correctness and effectiveness of these methods, and also fully verify the function and influence of generator over-excitation limiter in full dynamic voltage stability research.展开更多
The realization of protein functional movement is usually accompanied by specific conformational changes,and there exist some key residues that mediate and control the functional motions of proteins in the allosteric ...The realization of protein functional movement is usually accompanied by specific conformational changes,and there exist some key residues that mediate and control the functional motions of proteins in the allosteric process.In the present work,the perturbation-response scanning method developed by our group was combined with the molecular dynamics(MD)simulation to identify the key residues controlling the functional movement of proteins.In our method,a physical quantity that is directly related to protein specific function was introduced,and then based on the MD simulation trajectories,the perturbation-response scanning method was used to identify the key residues for functional motions,in which the residues that highly correlated with the fluctuation of the function-related quantity were identified as the key residues controlling the specific functional motions of the protein.Two protein systems,i.e.,the heat shock protein 70 and glutamine binding protein,were selected as case studies to validate the effectiveness of our method.Our calculated results are in good agreement with the experimental results.The location of the key residues in the two proteins are similar,indicating the similar mechanisms behind the performance of their biological functions.展开更多
In this study, the terahertz time-domain spectroscopy (THz-TDS) of crystalline methedrine, which is one of the illegal drugs, is performed using molecular dynamics simulation by the Fourier transform of time derivativ...In this study, the terahertz time-domain spectroscopy (THz-TDS) of crystalline methedrine, which is one of the illegal drugs, is performed using molecular dynamics simulation by the Fourier transform of time derivative auto-correlation functions of the dipole moment. In order to accurately detect the drugs from samples, it is necessary to build a complete database for terahertz spectra under different external conditions from theoretical calculation, which are hardly obtained from the experiments directly. Our results show remarkable consistency with the available experimental data in the frequency range of 10 - 100 cm-1 indicating that the presented method has significant capability to simulate terahertz spectra at various conditions. We investigated the effects of temperature and pressure on THz-TDS by simulating the system at temperature range between 78.4 K and 400 K at pressures up to 100 atm. Results show the spectral features of THz-TDS both in intensity and profile are highly sensitive to the variation of temperature and with a lower magnitude to the variation of pressure. The vanishing, rebuilding and shifting of spectral peaks are due to the complex mechanisms such as the anharmonicity, shifting in the vibration energy levels, formation and destruction of hydrogen-binding and the deformation of the potential energy surface during the environment changing. This improved our understanding for complicated THz-TDS of crystalline methedrine and would be useful for assignment of the practical measurements.展开更多
In order to explore the influence of welding parameters and to investigate the Al alloy (AA) nugget formation process, a comprehensive model involving electrical-thermal-mechanical and metallurgical analysis was estab...In order to explore the influence of welding parameters and to investigate the Al alloy (AA) nugget formation process, a comprehensive model involving electrical-thermal-mechanical and metallurgical analysis was established to numerically display the resistance spot welding (RSW) process within multiple fields and understand the AA-RSW physics. A multi-disciplinary finite element method (FEM) framework and a empirical sub-model were built to analyze the affecting factors on weld nugget and the underlying nature of welding physics with dynamic simulation procedure. Specifically, a counter-intuitive phenomenon of the resistance time-variation caused by the transient inverse virtual variation (TIVV) effect was highlighted and analyzed on the basis of welding current and temperature distribution simulation. The empirical model describing the TIVV phenomenon was used for modifying the dynamic resistance simulation during the AA spot welding process. The numerical and experimental results show that the proposed multi-field FEM model agrees with the measured AA welding feature, and the modified dynamic resistance model captures the physics of nugget growth and the electrical-thermal behavior under varying welding current and fluctuating heat input.展开更多
Computational Fluid Dynamics(CFD)simulation is one of the important methods to study the performance and influencing factors of turbine flow sensors.According to the working characteristics of the turbine flow sensor,...Computational Fluid Dynamics(CFD)simulation is one of the important methods to study the performance and influencing factors of turbine flow sensors.According to the working characteristics of the turbine flow sensor,the passive simulation method based on the six degrees of freedom(6-DOF)model and dynamic mesh is proposed in this paper.The reliability of the simulation method is verified by steady-state experiments and unsteady-state experiments.The results show that the trend of meter factor with flow rate acquired from the simulation is close to the experimental results,and the deviation between the simulation result and the experiment result is low with a maximum deviation of 2.88%.In the unsteady simulation study,the impeller speed changes with the inlet velocity of the turbine flow sensor,which has a good follow-up.The passive simulation method can be used to predict the dynamic performance of the turbine flow sensor.展开更多
In this paper. :LDDA (Lagrangian Discontinuous Deformation Analysis) method is used in modeling thedynamic process of the M,=7.8 Tang shan earthquake on July 28, 1976 and obtain directly the dynamic and quasi static d...In this paper. :LDDA (Lagrangian Discontinuous Deformation Analysis) method is used in modeling thedynamic process of the M,=7.8 Tang shan earthquake on July 28, 1976 and obtain directly the dynamic and quasi static dislocations. shear stress drops, fracture velocities of the Tang shan earthquake fault. The simulation showsthai the slip history at each point of the fault is different. The displacement vectors at the concave side of the faultis greater than that of the convex side of the fault. The 'over shoot' of the fault slip is greatest at the middle part ofthe fault and attenuates to its ends. The rupture velocities of the fault from the epicenter towards south-west andtowards north-east are 3.08 m/s and 1. 18 m/s, respectively, the average one is 2.13 In/s. The maximum dynamic.m quasi-static dislocations are 7. 1 m and 6.2 m respectively. the average quasi-static one on the fault is 4.5 m.initial stress dynamic and quasi-static shear stress drops are 8.1 M Pa and 5.4 MP4 respectively, the averagequasi-static shear stress drop is 3.9 M Pa. We found that the rupture velocities and shear stress are related to theinitial stress states of the fault.展开更多
The level of deformation development of surrounding rocks is a vital predictor to evaluate impending coal mine disasters and it is important to establish accurate measurements of the deformed status to ensure coal min...The level of deformation development of surrounding rocks is a vital predictor to evaluate impending coal mine disasters and it is important to establish accurate measurements of the deformed status to ensure coal mine safety. Traditional deformation monitoring methods are mostly based on single parameter, in this paper, multiple approaches are integrated: firstly, both electric and elastic models are established,from which electric field distribution and seismic wave recording are calculated and finally, the resistivity profiles and source position information are determined using inversion methods, from which then the deformation and failure of mine floor are evaluated. According to the inversion results of both electric and seismic field signals, multiple-parameter dynamic monitoring of surrounding rock deformation in deep mine can be performed. The methodology is validated using numerical simulation results which shows that the multi-parameter dynamic monitoring methods have better results for surrounding rock deformation in deep mine monitoring than single parameter methods.展开更多
A simulation method based on the lumped mass model is proposed for determining the dynamic behavior of nets exposed to a uniform current. Every mesh bar is modeled by a linear bar clement. The lumped mass point is set...A simulation method based on the lumped mass model is proposed for determining the dynamic behavior of nets exposed to a uniform current. Every mesh bar is modeled by a linear bar clement. The lumped mass point is set at the ends of each element. The net can be simulated by a discretized model consisting of many point masses and elements without mass. 3D shapes and the distribution of tensions of the net at different moments can be found from time integration of a set of motion equations with a computer program. Two nets are simulated according to reference experiments. Calculated results are in accordance with experimental results. The method is applicable and can be applied to improving design of, and research into other flexible structures, such as net cages.展开更多
To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters of nasal structure, three-dimensional, anatomically accurate representations of 30 adult nasal cavity models...To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters of nasal structure, three-dimensional, anatomically accurate representations of 30 adult nasal cavity models were recons- tructed based on processed tomography images collected from normal people. The airflow fields in nasal cavities were simulated by fluid dynamics with finite element software ANSYS. The results showed that the difference of human nasal cavity structure led to different airflow distribution in the nasal cavities and variation of the main airstream passing through the common nasal meatus. The nasal resistance in the regions of nasal valve and nasal vestibule accounted for more than half of the overall resistance. The characteristic model of nasal cavity was extracted on the basis of characteristic points and dimensions deduced from the original models. It showed that either the geometric structure or the airflow field of the two kinds of models was similar. The characteristic dimensions were the characteristic parameters of nasal cavity that could properly represent the original model in model studies on nasal cavity.展开更多
For studying the dynamic performance of subsea umbilical cable laying system and achieving the goal of cable tension and laying speed control,the rigid finite element method is used to discrete and transform the syste...For studying the dynamic performance of subsea umbilical cable laying system and achieving the goal of cable tension and laying speed control,the rigid finite element method is used to discrete and transform the system into a rigid-flexible coupling multi-body system which consists of rigid elements and spring-damping elements.The mathematical model of subsea umbilical cable laying system kinematic chain is presented with the second order Lagrange equation in the joint coordinate system,and dynamic modeling and simulation is performed with ADAMS.The dynamic analysis is conducted assuming the following three statuses:ideal laying,practical laying under wave disturbance,and practical laying with tension compensation.Results show that motion disturbances of the laying budge under sea waves,especially with heaving and pitching,will cause relatively serious fluctuations in cable tension and laying speed.Tension compensation,i.e.,active back tension torque control can restrict continuous tension increasing or decreasing effectively and rapidly,thus avoiding cable breach or buckling.展开更多
A first principles-based dynamic model for a continuous catalyst regeneration (CCR) platforming process, the UOP commercial naphtha catalytic reforming process, is developed in this paper. The lumping details of the n...A first principles-based dynamic model for a continuous catalyst regeneration (CCR) platforming process, the UOP commercial naphtha catalytic reforming process, is developed in this paper. The lumping details of the naphtha feed and reaction scheme of the reaction model are given. The process model is composed of the reforming reaction model with catalyst deactivation, the furnace model and the separator model, which is capable of capturing the major dynamics that occurs in this process system. Dynamic simulations are performed based on Gear numerical algorithm and method of lines (MOL), a numerical technique dealing with partial differential equations (PDEs). The results of simulation are also presented. Dynamic responses caused by disturbances in the process system can be correctly predicted through simulations.展开更多
Accurate 3-D fracture network model for rock mass in dam foundation is of vital importance for stability,grouting and seepage analysis of dam foundation.With the aim of reducing deviation between fracture network mode...Accurate 3-D fracture network model for rock mass in dam foundation is of vital importance for stability,grouting and seepage analysis of dam foundation.With the aim of reducing deviation between fracture network model and measured data,a 3-D fracture network dynamic modeling method based on error analysis was proposed.Firstly,errors of four fracture volume density estimation methods(proposed by ODA,KULATILAKE,MAULDON,and SONG)and that of four fracture size estimation methods(proposed by EINSTEIN,SONG and TONON)were respectively compared,and the optimal methods were determined.Additionally,error index representing the deviation between fracture network model and measured data was established with integrated use of fractal dimension and relative absolute error(RAE).On this basis,the downhill simplex method was used to build the dynamic modeling method,which takes the minimum of error index as objective function and dynamically adjusts the fracture density and size parameters to correct the error index.Finally,the 3-D fracture network model could be obtained which meets the requirements.The proposed method was applied for 3-D fractures simulation in Miao Wei hydropower project in China for feasibility verification and the error index reduced from 2.618 to 0.337.展开更多
Heat conduction in single-walled carbon nanotubes （SWCNTs） has been investigated by using various methods, while less work has been focused on multi-walled carbon nanotubes （MWCNTs）. The thermal conductivities of ...Heat conduction in single-walled carbon nanotubes （SWCNTs） has been investigated by using various methods, while less work has been focused on multi-walled carbon nanotubes （MWCNTs）. The thermal conductivities of the double-walled carbon nanotubes （DWCNTs） with two different temperature control methods are studied by using molecular dynamics （MD） simulations. One case is that the heat baths （HBs） are imposed only on the outer wall, while the other is that the HBs are imposed on both the two walls. The results show that the ratio of the thermal conductivity of DWCNTs in the first case to that in the second case is inversely proportional to the ratio of the cross-sectional area of the DWCNT to that of its outer wall. In order to interpret the results and explore the heat conduction mechanisms, the inter-wall thermal transport of DWCNTs is simulated. Analyses of the temperature profiles of a DWCNT and its two walls in the two cases and the inter- wall thermal resistance show that in the first case heat is almost transported only along the outer wall, while in the second case a DWCNT behaves like parallel heat transport channels in which heat is transported along each wall independently. This gives a good explanation of our results and presents the heat conduction mechanisms of MWCNTs.展开更多
This paper analyzes characteristics of multi type current transformers hybrid operation for each branch of the bus and their effects on differential protection of the bus. By theoretically analyzing transmission chara...This paper analyzes characteristics of multi type current transformers hybrid operation for each branch of the bus and their effects on differential protection of the bus. By theoretically analyzing transmission characteristics of multi type current transformers and their influence factors, we study the dynamic model testing method of multi type current transformers for the bus, and design 3 kinds of testing schemes by making the equivalent model based on the field of P-level current transformer, TPY-level current transformer and electronic current transformer, and build the hybrid operation testing platform of multi type current transformers. Finally, we compare and analyze the transmission characteristics difference of multi type current transformers on the same branch and the characteristics difference of hybrid operation in two successive external faults, analyze the cause behind the differences, and put forward the corresponding improvement measures.展开更多
In this paper, simulation of InAs/GaAs quantum dot (QD) laser is performed based upon a set of eight rate equations for the carriers and photons in five energy states. Carrier dynamics in these lasers were under analy...In this paper, simulation of InAs/GaAs quantum dot (QD) laser is performed based upon a set of eight rate equations for the carriers and photons in five energy states. Carrier dynamics in these lasers were under analysis and the rate equations are solved using 4th order Runge-Kutta method. We have shown that by increasing injected current to the active medium of laser, switching-on and stability time of the system would decrease and power peak and stationary power will be increased. Also, emission in any state will start when the lower state is saturated and remain steady. The results including P-I characteristic curve for the ground state (GS), first excited state (ES1), second excited state (ES2) and output power of the QD laser will be presented.展开更多
The possibility of complex formation by short lysine brush and therapeutic Semax peptides was investigated using molecular dynamics method. Lysine dendrimers and polymer brushes are used for drug and other (e.g., DNA,...The possibility of complex formation by short lysine brush and therapeutic Semax peptides was investigated using molecular dynamics method. Lysine dendrimers and polymer brushes are used for drug and other (e.g., DNA, peptides, and polysaccharides) molecules delivery to different target cells. It is known that they could penetrate blood brain barrier. Since short lysine brush is nontoxic, a system containing of such brush and 8 oppositely charged Semax peptides was studied. It was obtained that stable complexes consisting of brush and peptides formed and structures of these complexes were investigated. Such complex can be used in future for delivery of Semax peptides to brain since these peptides have significant antioxidant, antihypoxic and neuroprotective effects.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11904036 and 12175081)Fundamental Research Funds for the Central Universities(Grant No.CCNU22QNOO4)。
文摘The human serotonin transporter(SERT)terminates neurotransmission by removing serotonin from the synaptic cleft,which is an essential process that plays an important role in depression.In addition to natural substrate serotonin,SERT is also the target of the abused drug cocaine and,clinically used antidepressants,escitalopram,and paroxetine.To date,few studies have attempted to investigate the unbinding mechanism underlying the orthosteric and allosteric modulation of SERT.In this article,the conserved property of the orthosteric and allosteric sites(S1 and S2)of SERT was revealed by combining the high resolutions of x-ray crystal structures and molecular dynamics(MD)simulations.The residues Tyr95 and Ser438 located within the S1 site,and Arg104 located within the S2 site in SERT illustrate conserved interactions(hydrogen bonds and hydrophobic interactions),as responses to selective serotonin reuptake inhibitors.Van der Waals interactions were keys to designing effective drugs inhibiting SERT and further,electrostatic interactions highlighted escitalopram as a potent antidepressant.We found that cocaine,escitalopram,and paroxetine,whether the S1 site or the S2 site,were more competitive.According to this potential of mean force(PMF)simulations,the new insights reveal the principles of competitive inhibitors that lengths of trails from central SERT to an opening were~18A for serotonin and~22 A for the above-mentioned three drugs.Furthermore,the distance between the natural substrate serotonin and cocaine(or escitalopram)at the allosteric site was~3A.Thus,it can be inferred that the potent antidepressants tended to bind at deeper positions of the S1 or the S2 site of SERT in comparison to the substrate.Continuing exploring the processes of unbinding four ligands against the two target pockets of SERT,this study observed a broad pathway in which serotonin,cocaine,escitalopram(at the S1 site),and paroxetine all were pulled out to an opening between MT1b and MT6a,which may be helpful to understand the dissociation mechanism of antidepressants.
基金Project(41630642)supported by the Key Project of National Natural Science Foundation of ChinaProject(51974360)supported by the National Natural Science Foundation of ChinaProject(2018JJ3656)supported by the Natural Science Foundation of Hunan Province,China。
文摘In the context of deep rock engineering,the in-situ stress state is of major importance as it plays an important role in rock dynamic response behavior.Thus,stress initialization becomes crucial and is the first step for the dynamic response simulation of rock mass in a high in-situ stress field.In this paper,stress initialization methods,including their principles and operating procedures for reproducing steady in-situ stress state in LS-DYNA,are first introduced.Then the most popular four methods,i.e.,explicit dynamic relaxation(DR)method,implicit-explicit sequence method,Dynain file method and quasi-static method,are exemplified through a case analysis by using the RHT and plastic hardening rock material models to simulate rock blasting under in-situ stress condition.Based on the simulations,it is concluded that the stress initialization results obtained by implicit-explicit sequence method and dynain file method are closely related to the rock material model,and the explicit DR method has an obvious advantage in solution time when compared to other methods.Besides that,it is recommended to adopt two separate analyses for the whole numerical simulation of rock mass under the combined action of in-situ stress and dynamic disturbance.
文摘The structure and properties of molten salt solution o J Li,K|F,Cl system have been investiged by computerized simulation of molecular dynamic method.The partial RDF,the partial molar energy of mixing and the diffusion coeffients of Li^+,K^+,F^- and Cl^- have been calculated. The results are in agreement with the experimental values.The regularities of the distribution of ions and mieroscopic holes are discussed based on the results of computerized simulation.
文摘The computational methods of a typical dynamic mathematical model that can describe the differential element and the inertial element for the system simulation are researched. The stability of numerical solutions of the dynamic mathematical model is researched. By means of theoretical analysis, the error formulas, the error sign criteria and the error relationship criterion of the implicit Euler method and the trapezoidal method are given, the dynamic factor affecting the computational accuracy has been found, the formula and the methods of computing the dynamic factor are given. The computational accuracy of the dynamic mathematical model like this can be improved by use of the dynamic factor.
文摘The voltage stability is substantially a dynamic stability, but the primary method which is more mature and engineering practical to analyze the stability of voltage is still static analysis. The time-domain simulation is an important measure in research of complex power grid. With the development of full dynamic simulation technology, the research of dynamic voltage stability by using full dynamic simulation program which is based on time-domain simulation can be carried out. This paper uses full dynamic simulation program in dynamic voltage stability research, lays special stress on research in how generator over-excitation limiter functioned and influence in dynamic voltage stability research, and raise 2 methods and steps to figure out dynamic stable voltage in both over-excitation counted and not counted. The simulation results of examples indicate the correctness and effectiveness of these methods, and also fully verify the function and influence of generator over-excitation limiter in full dynamic voltage stability research.
文摘The realization of protein functional movement is usually accompanied by specific conformational changes,and there exist some key residues that mediate and control the functional motions of proteins in the allosteric process.In the present work,the perturbation-response scanning method developed by our group was combined with the molecular dynamics(MD)simulation to identify the key residues controlling the functional movement of proteins.In our method,a physical quantity that is directly related to protein specific function was introduced,and then based on the MD simulation trajectories,the perturbation-response scanning method was used to identify the key residues for functional motions,in which the residues that highly correlated with the fluctuation of the function-related quantity were identified as the key residues controlling the specific functional motions of the protein.Two protein systems,i.e.,the heat shock protein 70 and glutamine binding protein,were selected as case studies to validate the effectiveness of our method.Our calculated results are in good agreement with the experimental results.The location of the key residues in the two proteins are similar,indicating the similar mechanisms behind the performance of their biological functions.
文摘In this study, the terahertz time-domain spectroscopy (THz-TDS) of crystalline methedrine, which is one of the illegal drugs, is performed using molecular dynamics simulation by the Fourier transform of time derivative auto-correlation functions of the dipole moment. In order to accurately detect the drugs from samples, it is necessary to build a complete database for terahertz spectra under different external conditions from theoretical calculation, which are hardly obtained from the experiments directly. Our results show remarkable consistency with the available experimental data in the frequency range of 10 - 100 cm-1 indicating that the presented method has significant capability to simulate terahertz spectra at various conditions. We investigated the effects of temperature and pressure on THz-TDS by simulating the system at temperature range between 78.4 K and 400 K at pressures up to 100 atm. Results show the spectral features of THz-TDS both in intensity and profile are highly sensitive to the variation of temperature and with a lower magnitude to the variation of pressure. The vanishing, rebuilding and shifting of spectral peaks are due to the complex mechanisms such as the anharmonicity, shifting in the vibration energy levels, formation and destruction of hydrogen-binding and the deformation of the potential energy surface during the environment changing. This improved our understanding for complicated THz-TDS of crystalline methedrine and would be useful for assignment of the practical measurements.
基金Projects (11202125, 61175038) supported by the National Natural Science Foundation of China
文摘In order to explore the influence of welding parameters and to investigate the Al alloy (AA) nugget formation process, a comprehensive model involving electrical-thermal-mechanical and metallurgical analysis was established to numerically display the resistance spot welding (RSW) process within multiple fields and understand the AA-RSW physics. A multi-disciplinary finite element method (FEM) framework and a empirical sub-model were built to analyze the affecting factors on weld nugget and the underlying nature of welding physics with dynamic simulation procedure. Specifically, a counter-intuitive phenomenon of the resistance time-variation caused by the transient inverse virtual variation (TIVV) effect was highlighted and analyzed on the basis of welding current and temperature distribution simulation. The empirical model describing the TIVV phenomenon was used for modifying the dynamic resistance simulation during the AA spot welding process. The numerical and experimental results show that the proposed multi-field FEM model agrees with the measured AA welding feature, and the modified dynamic resistance model captures the physics of nugget growth and the electrical-thermal behavior under varying welding current and fluctuating heat input.
基金supported by National Natural Science Foundation of China,China(62173122)Hebei Key Project of Natural Science Foundation(F2021201031)Beijing-Tianjin-Hebei Collaborative Innovation Community Construction Project(20540301D)
文摘Computational Fluid Dynamics(CFD)simulation is one of the important methods to study the performance and influencing factors of turbine flow sensors.According to the working characteristics of the turbine flow sensor,the passive simulation method based on the six degrees of freedom(6-DOF)model and dynamic mesh is proposed in this paper.The reliability of the simulation method is verified by steady-state experiments and unsteady-state experiments.The results show that the trend of meter factor with flow rate acquired from the simulation is close to the experimental results,and the deviation between the simulation result and the experiment result is low with a maximum deviation of 2.88%.In the unsteady simulation study,the impeller speed changes with the inlet velocity of the turbine flow sensor,which has a good follow-up.The passive simulation method can be used to predict the dynamic performance of the turbine flow sensor.
文摘In this paper. :LDDA (Lagrangian Discontinuous Deformation Analysis) method is used in modeling thedynamic process of the M,=7.8 Tang shan earthquake on July 28, 1976 and obtain directly the dynamic and quasi static dislocations. shear stress drops, fracture velocities of the Tang shan earthquake fault. The simulation showsthai the slip history at each point of the fault is different. The displacement vectors at the concave side of the faultis greater than that of the convex side of the fault. The 'over shoot' of the fault slip is greatest at the middle part ofthe fault and attenuates to its ends. The rupture velocities of the fault from the epicenter towards south-west andtowards north-east are 3.08 m/s and 1. 18 m/s, respectively, the average one is 2.13 In/s. The maximum dynamic.m quasi-static dislocations are 7. 1 m and 6.2 m respectively. the average quasi-static one on the fault is 4.5 m.initial stress dynamic and quasi-static shear stress drops are 8.1 M Pa and 5.4 MP4 respectively, the averagequasi-static shear stress drop is 3.9 M Pa. We found that the rupture velocities and shear stress are related to theinitial stress states of the fault.
基金financial support from the Fundamental Research Funds for the Central Universities of China (No. 2015QNB19)the financial support from the Open Fund of Key Laboratory of Safety and High-efficiency Coal Mining, Ministry of Education of China (No. JYBSYS2015107)+2 种基金the National Natural Science Foundation of China (Nos. 51404254, 41430317 and U1261202)the China Postdoctoral Science Foundation of China (No. 2014M560465)the Jiangsu Planned Projects for Postdoctoral Research Funds of China (No. 1302050B)
文摘The level of deformation development of surrounding rocks is a vital predictor to evaluate impending coal mine disasters and it is important to establish accurate measurements of the deformed status to ensure coal mine safety. Traditional deformation monitoring methods are mostly based on single parameter, in this paper, multiple approaches are integrated: firstly, both electric and elastic models are established,from which electric field distribution and seismic wave recording are calculated and finally, the resistivity profiles and source position information are determined using inversion methods, from which then the deformation and failure of mine floor are evaluated. According to the inversion results of both electric and seismic field signals, multiple-parameter dynamic monitoring of surrounding rock deformation in deep mine can be performed. The methodology is validated using numerical simulation results which shows that the multi-parameter dynamic monitoring methods have better results for surrounding rock deformation in deep mine monitoring than single parameter methods.
基金This project was financially supported by the High Technology Research and Development Program of China (GrantNo.2001AA623030 and No.2003AA623030)
文摘A simulation method based on the lumped mass model is proposed for determining the dynamic behavior of nets exposed to a uniform current. Every mesh bar is modeled by a linear bar clement. The lumped mass point is set at the ends of each element. The net can be simulated by a discretized model consisting of many point masses and elements without mass. 3D shapes and the distribution of tensions of the net at different moments can be found from time integration of a set of motion equations with a computer program. Two nets are simulated according to reference experiments. Calculated results are in accordance with experimental results. The method is applicable and can be applied to improving design of, and research into other flexible structures, such as net cages.
基金the National Natural Science Foundation of China (1047202510672036)the Natural Science Foundation of Liaoning Province,China (20032109)
文摘To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters of nasal structure, three-dimensional, anatomically accurate representations of 30 adult nasal cavity models were recons- tructed based on processed tomography images collected from normal people. The airflow fields in nasal cavities were simulated by fluid dynamics with finite element software ANSYS. The results showed that the difference of human nasal cavity structure led to different airflow distribution in the nasal cavities and variation of the main airstream passing through the common nasal meatus. The nasal resistance in the regions of nasal valve and nasal vestibule accounted for more than half of the overall resistance. The characteristic model of nasal cavity was extracted on the basis of characteristic points and dimensions deduced from the original models. It showed that either the geometric structure or the airflow field of the two kinds of models was similar. The characteristic dimensions were the characteristic parameters of nasal cavity that could properly represent the original model in model studies on nasal cavity.
基金Supported by the National Science and Technology Major Project:Development of Large Oil-gas Fields&Coal-bed Methane(No.2011ZX05056)
文摘For studying the dynamic performance of subsea umbilical cable laying system and achieving the goal of cable tension and laying speed control,the rigid finite element method is used to discrete and transform the system into a rigid-flexible coupling multi-body system which consists of rigid elements and spring-damping elements.The mathematical model of subsea umbilical cable laying system kinematic chain is presented with the second order Lagrange equation in the joint coordinate system,and dynamic modeling and simulation is performed with ADAMS.The dynamic analysis is conducted assuming the following three statuses:ideal laying,practical laying under wave disturbance,and practical laying with tension compensation.Results show that motion disturbances of the laying budge under sea waves,especially with heaving and pitching,will cause relatively serious fluctuations in cable tension and laying speed.Tension compensation,i.e.,active back tension torque control can restrict continuous tension increasing or decreasing effectively and rapidly,thus avoiding cable breach or buckling.
文摘A first principles-based dynamic model for a continuous catalyst regeneration (CCR) platforming process, the UOP commercial naphtha catalytic reforming process, is developed in this paper. The lumping details of the naphtha feed and reaction scheme of the reaction model are given. The process model is composed of the reforming reaction model with catalyst deactivation, the furnace model and the separator model, which is capable of capturing the major dynamics that occurs in this process system. Dynamic simulations are performed based on Gear numerical algorithm and method of lines (MOL), a numerical technique dealing with partial differential equations (PDEs). The results of simulation are also presented. Dynamic responses caused by disturbances in the process system can be correctly predicted through simulations.
基金Project(51321065)supported by the Innovative Research Groups of the National Natural Science Foundation of ChinaProject(2013CB035904)supported by the National Basic Research Program of China(973 Program)Project(51439005)supported by the National Natural Science Foundation of China
文摘Accurate 3-D fracture network model for rock mass in dam foundation is of vital importance for stability,grouting and seepage analysis of dam foundation.With the aim of reducing deviation between fracture network model and measured data,a 3-D fracture network dynamic modeling method based on error analysis was proposed.Firstly,errors of four fracture volume density estimation methods(proposed by ODA,KULATILAKE,MAULDON,and SONG)and that of four fracture size estimation methods(proposed by EINSTEIN,SONG and TONON)were respectively compared,and the optimal methods were determined.Additionally,error index representing the deviation between fracture network model and measured data was established with integrated use of fractal dimension and relative absolute error(RAE).On this basis,the downhill simplex method was used to build the dynamic modeling method,which takes the minimum of error index as objective function and dynamically adjusts the fracture density and size parameters to correct the error index.Finally,the 3-D fracture network model could be obtained which meets the requirements.The proposed method was applied for 3-D fractures simulation in Miao Wei hydropower project in China for feasibility verification and the error index reduced from 2.618 to 0.337.
基金supported by the National Natural Science Foundation of China(Grant Nos.51322603,51136001,and 51356001)the Program for New Century Excellent Talents in University,Science Fund for Creative Research Groups of China(Grant No.51321002)the Initiative Scientific Research Program of Tsinghua University,China
文摘Heat conduction in single-walled carbon nanotubes （SWCNTs） has been investigated by using various methods, while less work has been focused on multi-walled carbon nanotubes （MWCNTs）. The thermal conductivities of the double-walled carbon nanotubes （DWCNTs） with two different temperature control methods are studied by using molecular dynamics （MD） simulations. One case is that the heat baths （HBs） are imposed only on the outer wall, while the other is that the HBs are imposed on both the two walls. The results show that the ratio of the thermal conductivity of DWCNTs in the first case to that in the second case is inversely proportional to the ratio of the cross-sectional area of the DWCNT to that of its outer wall. In order to interpret the results and explore the heat conduction mechanisms, the inter-wall thermal transport of DWCNTs is simulated. Analyses of the temperature profiles of a DWCNT and its two walls in the two cases and the inter- wall thermal resistance show that in the first case heat is almost transported only along the outer wall, while in the second case a DWCNT behaves like parallel heat transport channels in which heat is transported along each wall independently. This gives a good explanation of our results and presents the heat conduction mechanisms of MWCNTs.
文摘This paper analyzes characteristics of multi type current transformers hybrid operation for each branch of the bus and their effects on differential protection of the bus. By theoretically analyzing transmission characteristics of multi type current transformers and their influence factors, we study the dynamic model testing method of multi type current transformers for the bus, and design 3 kinds of testing schemes by making the equivalent model based on the field of P-level current transformer, TPY-level current transformer and electronic current transformer, and build the hybrid operation testing platform of multi type current transformers. Finally, we compare and analyze the transmission characteristics difference of multi type current transformers on the same branch and the characteristics difference of hybrid operation in two successive external faults, analyze the cause behind the differences, and put forward the corresponding improvement measures.
文摘In this paper, simulation of InAs/GaAs quantum dot (QD) laser is performed based upon a set of eight rate equations for the carriers and photons in five energy states. Carrier dynamics in these lasers were under analysis and the rate equations are solved using 4th order Runge-Kutta method. We have shown that by increasing injected current to the active medium of laser, switching-on and stability time of the system would decrease and power peak and stationary power will be increased. Also, emission in any state will start when the lower state is saturated and remain steady. The results including P-I characteristic curve for the ground state (GS), first excited state (ES1), second excited state (ES2) and output power of the QD laser will be presented.
文摘The possibility of complex formation by short lysine brush and therapeutic Semax peptides was investigated using molecular dynamics method. Lysine dendrimers and polymer brushes are used for drug and other (e.g., DNA, peptides, and polysaccharides) molecules delivery to different target cells. It is known that they could penetrate blood brain barrier. Since short lysine brush is nontoxic, a system containing of such brush and 8 oppositely charged Semax peptides was studied. It was obtained that stable complexes consisting of brush and peptides formed and structures of these complexes were investigated. Such complex can be used in future for delivery of Semax peptides to brain since these peptides have significant antioxidant, antihypoxic and neuroprotective effects.
