Despite the expansive applications of gas-phase unfolding techniques,the molecular mechanism for the solvent-free forced unfolding pathway which substrate multidomain proteins usually adopt remains elusive at the seco...Despite the expansive applications of gas-phase unfolding techniques,the molecular mechanism for the solvent-free forced unfolding pathway which substrate multidomain proteins usually adopt remains elusive at the secondary structure level.Herein,upon carefully selecting CRM_(197) as a therapeutically-relevant model system containing multiple secondary structure-separated domains,we systematically examine its solvent-free unfolding pathway.Further-more,utilizing the hybrid of noncovalent chemical probing with niacinamide and ion mobility-mass spectrometry-guided all-atom molecular dynamics simulations,we map a nearly complete unfolding atlas for the conjugate vaccine carrier protein CRM_(197) in a domain-and secondary structure-resolved manner.The totality of our data supports the preferential unfolding of the sheet-rich domain,indicating the dynamic transition from β-sheet toα-helix,and demonstrating that helix exhibit comparatively higher stability thanβ-sheets.We propose that this sheet-to-helix dynamic transition may be central to the gas-phase unfolding pathways of multidomain proteins,suggesting the need for systematic studies on additional multidomain protein systems.展开更多
Spectrin domains,characterized by a distinctive triple helix structure,are crucial in physiological processes,particularly in maintaining membrane shape and crosslinking cytoskeletons.Previous research on the 16th dom...Spectrin domains,characterized by a distinctive triple helix structure,are crucial in physiological processes,particularly in maintaining membrane shape and crosslinking cytoskeletons.Previous research on the 16th domain of a-spectrin repeats(R16)has yielded conflicting results:bulk experiments showed an unfolding rate approximately two orders of magnitude faster than the zero-force result extrapolated from single-molecule force spectroscopy experiments using atomic force microscopy(AFM).To address this discrepancy,we investigated the folding and unfolding rates of R16 across a broader range of forces using magnetic tweezers(MT).Our findings reveal that AFM results at higher forces cannot be directly extrapolated to the low-force regime due to a nonlinear relationship between force and the logarithm of the unfolding rate.We demonstrated that two-dimensional model,structural-elastic model,and two-pathway model can all effectively explain the experimental data when they capture the core physics of the short unfolding distance at low forces.Our study provides a more comprehensive understanding of the unfolding dynamics of the spectrin domain,resolves previous contradictory experimental results,and highlights the common basis of different theoretical models.展开更多
In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the re...In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the relationship between the experimental and simulation results were explored.Our computational findings on the secondary structure of SEB showed that at room temperature,the CD spectroscopic results were highly consistent with the MD results.Moreover,under heating conditions,the changing trends of helix,sheet and random coil obtained by CD spectral fitting were highly consistent with those obtained by MD.In order to gain a deeper understanding of the thermal stability mechanism of SEB,the MD trajectories were analyzed in terms of root mean square deviation(RMSD),secondary structure assignment(SSA),radius of gyration(R_(g)),free energy surfaces(FES),solvent-accessible surface area(SASA),hydrogen bonds and salt bridges.The results showed that at low heating temperature,domain Ⅰ without loops(omitting the mobile loop region)mainly relied on hydrophobic interaction to maintain its thermal stability,whereas the thermal stability of domain Ⅱ was mainly controlled by salt bridges and hydrogen bonds.Under high heating temperature conditions,the hydrophobic interactions in domain Ⅰ without loops were destroyed and the secondary structure was almost completely lost,while domain Ⅱ could still rely on salt bridges as molecular staples to barely maintain the stability of the secondary structure.These results help us to understand the thermodynamic and kinetic mechanisms that maintain the thermal stability of SEB at the molecular level,and provide a direction for establishing safer and more effective food sterilization processes.展开更多
In an attempt to realize a flapping wing micro-air vehicle with morphing wings, we report on improvements to our previousfoldable artificial hind wing.Multiple hinges, which were implemented to mimic the bending zone ...In an attempt to realize a flapping wing micro-air vehicle with morphing wings, we report on improvements to our previousfoldable artificial hind wing.Multiple hinges, which were implemented to mimic the bending zone of a beetle hind wing, weremade of small composite hinge plates and tiny aluminum rivets.The buck-tails of rivets were flared after the hinge plates wereassembled with the rivets so that the folding/unfolding motions could be completed in less time, and the straight shape of theartificial hind wing could be maintained after fabrication.Folding and unfolding actions were triggered by electrically-activatedShape Memory Alloy (SMA) wires.For wing folding, the actuation characteristics of the SMA wire actuator were modifiedthrough heat treatment.Through a series of flapping tests, we confirmed that the artificial wings did not fold back and arbitrarilyfluctuate during the flapping motion.展开更多
A self-adaptive differential evolution neutron spectrum unfolding algorithm(SDENUA)is established in this study to unfold the neutron spectra obtained from a water-pumping-injection multilayered concentric sphere neut...A self-adaptive differential evolution neutron spectrum unfolding algorithm(SDENUA)is established in this study to unfold the neutron spectra obtained from a water-pumping-injection multilayered concentric sphere neutron spectrometer(WMNS).Specifically,the neutron fluence bounds are estimated to accelerate the algorithm convergence,and the minimum error between the optimal solution and input neutron counts with relative uncertainties is limited to 10^(-6)to avoid unnecessary calculations.Furthermore,the crossover probability and scaling factor are self-adaptively controlled.FLUKA Monte Carlo is used to simulate the readings of the WMNS under(1)a spectrum of Cf-252 and(2)its spectrum after being moderated,(3)a spectrum used for boron neutron capture therapy,and(4)a reactor spectrum.Subsequently,the measured neutron counts are unfolded using the SDENUA.The uncertainties of the measured neutron count and the response matrix are considered in the SDENUA,which does not require complex parameter tuning or an a priori default spectrum.The results indicate that the solutions of the SDENUA agree better with the IAEA spectra than those of MAXED and GRAVEL in UMG 3.1,and the errors of the final results calculated using the SDENUA are less than 12%.The established SDENUA can be used to unfold spectra from the WMNS.展开更多
Determining the similarity degree between process models was very important for their management,reuse,and analysis.Current approaches either focused on process model's structural aspect,or had inefficiency or imp...Determining the similarity degree between process models was very important for their management,reuse,and analysis.Current approaches either focused on process model's structural aspect,or had inefficiency or imprecision in behavioral similarity.Aiming at these problems,a novel similarity measure which extended an existing method named Transition Adjacent Relation(TAR) with improved precision and efficiency named TAR * was proposed.The ability of measuring similarity was extended by eliminating the duplicate tasks without impacting the behaviors.For precision,TARs was classified into repeatable and unrepeatable ones to identify whether a TAR was involved in a loop.Two new kinds of TARs were added,one related to the invisible tasks after the source place and before sink place,and the other representing implicit dependencies.For efficiency,all TARs based on unfolding instead of its reach ability graph of a labeled Petri net were calculated to avoid state space explosion.Experiments on artificial and real-world process models showed the effectiveness and efficiency of the proposed method.展开更多
An accurate energy calibration of a 5＂× 2＂ BC501A liquid scintillator-based neutron detector by means of photon sources and the unfolding of pulse height spectra are described. The photon responses were measure...An accurate energy calibration of a 5＂× 2＂ BC501A liquid scintillator-based neutron detector by means of photon sources and the unfolding of pulse height spectra are described. The photon responses were measured with 22Na, 137Cs and 54Mn photon sources and simulated using the GRESP code, which was developed at the Physiknlisch Technische Bundesanstalt in Germany. Pulse height spectra produced by three different photon sources were employed to investigate the effects of the unfolding techniques. It was found that the four unfolding codes of the HEPRO and UMG3.3 packages, including GRAVEL, UNFANA, MIEKE and MAXED, performed well with the test spectra and produced generally consistent results. They could therefore be used to obtain neutron energy spectra in toknmak experiments.展开更多
Many biological functions of RNA molecules are re- lated to their pseudoknot structures. It is significant for predicting the structure and function of RNA that learning about the stability and the process of RNA pseu...Many biological functions of RNA molecules are re- lated to their pseudoknot structures. It is significant for predicting the structure and function of RNA that learning about the stability and the process of RNA pseudoknot folding and unfolding. The structural features of mouse mammary tumor virus （MMTV） RNA pseudoknot in different ion concentration, the unfolding process of the RNA pseudoknot, and the two hairpin helices that constitute the RNA pseudoknot were studied with all atom molecule dynam- ics simulation method in this paper. We found that the higher cation concentration can cause structure of the RNA molecules more stable, and ions played an indispensable role in keeping the structure of RNA molecules stable; the unfolding process of hair- pin structure was corresponding to the antiprocess of its folding process. The main pathway of pseudoknot unfolding was that the inner base pair opened first, and then, the two helices, which formed the RNA pseudoknot opened decussately, while the folding pathway of the RNA pseudoknot was a helix folding after forma- tion of the other helix. Therefore, the unfolding process of RNA pseudoknot is different from the antiprocess of its folding process, and the unfolding process of each helix in the RNA pseudoknot is similar to the hairpin structure＇s unfolding process, which means that both are the unzipping process.展开更多
The neutron spectrum unfolding by Bonner sphere spectrometer(BSS) is considered a complex multidimensional model,which requires complex mathematical methods to solve the first kind of Fredholm integral equation. In or...The neutron spectrum unfolding by Bonner sphere spectrometer(BSS) is considered a complex multidimensional model,which requires complex mathematical methods to solve the first kind of Fredholm integral equation. In order to solve the problem of the maximum likelihood expectation maximization(MLEM) algorithm which is easy to suffer the pitfalls of local optima and the particle swarm optimization(PSO) algorithm which is easy to get unreasonable flight direction and step length of particles, which leads to the invalid iteration and affect efficiency and accuracy, an improved PSO-MLEM algorithm, combined of PSO and MLEM algorithm, is proposed for neutron spectrum unfolding. The dynamic acceleration factor is used to balance the ability of global and local search, and improves the convergence speed and accuracy of the algorithm. Firstly, the Monte Carlo method was used to simulated the BSS to obtain the response function and count rates of BSS. In the simulation of count rate, four reference spectra from the IAEA Technical Report Series No. 403 were used as input parameters of the Monte Carlo method. The PSO-MLEM algorithm was used to unfold the neutron spectrum of the simulated data and was verified by the difference of the unfolded spectrum to the reference spectrum. Finally, the 252Cf neutron source was measured by BSS, and the PSO-MLEM algorithm was used to unfold the experimental neutron spectrum.Compared with maximum entropy deconvolution(MAXED), PSO and MLEM algorithm, the PSO-MLEM algorithm has fewer parameters and automatically adjusts the dynamic acceleration factor to solve the problem of local optima. The convergence speed of the PSO-MLEM algorithm is 1.4 times and 3.1 times that of the MLEM and PSO algorithms. Compared with PSO, MLEM and MAXED, the correlation coefficients of PSO-MLEM algorithm are increased by 33.1%, 33.5% and 1.9%, and the relative mean errors are decreased by 98.2%, 97.8% and 67.4%.展开更多
Src SH3 protein domain is a typical two-state protein which has been confirmed by research of denaturant-induced unfolding dynamics.Force spectroscopy experiments by optical tweezers and atomic force microscopy have m...Src SH3 protein domain is a typical two-state protein which has been confirmed by research of denaturant-induced unfolding dynamics.Force spectroscopy experiments by optical tweezers and atomic force microscopy have measured the force-dependent unfolding rates with different kinds of pulling geometry.However,the equilibrium folding and unfolding dynamics at constant forces has not been reported.Here,using stable magnetic tweezers,we performed equilibrium folding and unfolding dynamic measurement and force-jump measurement of src SH3 domain with tethering points at its N-and C-termini.From the obtained force-dependent transition rates,a detailed two-state free energy landscape of src SH3 protein is constructed with quantitative information of folding free energy,transition state barrier height and position,which exemplifies the capability of magnetic tweezers to study protein folding and unfolding dynamics.展开更多
To gain more understanding of cell-matrix adhesion,we consider an idealized theoretical model of a cluster of integrin-fibronectin bonds at the cell-matrix interface subjected to a dynamic ramping.The distributions of...To gain more understanding of cell-matrix adhesion,we consider an idealized theoretical model of a cluster of integrin-fibronectin bonds at the cell-matrix interface subjected to a dynamic ramping.The distributions of bond traction and interfacial deformation are assumed to obey classical elastic equations,whereas the dissociation/association of individual bonds as well as unfolding/refolding of fibronectin domains are described by stochastic equations.Through stochastic-elasticity coupling,we perform Monte Carlo simulations to investigate how the collective behavior and adhesion performance of the integrin-fibronectin-mediated interface are influenced by two characteristics newly incorporated in the modeling,i.e.,catchlike dissociation between integrin and fibronectin,and unfolding of repeated domains in fibronectin.The probable unfolding of fibronectin domains is found to have profound effects on the resultant adhesion energy of the integrin-fibronectin-mediated interface,and governs the failure model transiting between uniform decay and catastrophic crack-like rupture.展开更多
In this paper,the (?)-equivariant (s, t)-equivalence relation and (?)-equivariant infinitesimally (r, s)-stability of (?)-equivariant bifurcation problem are defined. The criterion for (?)-equivariant infinitesimally ...In this paper,the (?)-equivariant (s, t)-equivalence relation and (?)-equivariant infinitesimally (r, s)-stability of (?)-equivariant bifurcation problem are defined. The criterion for (?)-equivariant infinitesimally (r, s)-stability is proven when (?) is a compact finite Lie group .Transversality condition is used to characterize the stability.展开更多
For the unfolding of equivariant bifurcation problems with two types of state variables in the presence of parameter symmetry,the versal unfolding theorem with respect to left-right equivalence is obtained by using th...For the unfolding of equivariant bifurcation problems with two types of state variables in the presence of parameter symmetry,the versal unfolding theorem with respect to left-right equivalence is obtained by using the related methods and techniques in the singularity theory of smooth map-germs.The corresponding results in[4,9]can be considered as its special cases.A relationship between the versal unfolding w.r.t.left-right equivalence and the versal deformation w.r.t.contact equivalence is established.展开更多
Ultra-large plate forgings are foundation of heavy machinery,but many parts of the type cannot be made by conventional technologies due to the characters of extreme manufacturing in terms of size and quality requireme...Ultra-large plate forgings are foundation of heavy machinery,but many parts of the type cannot be made by conventional technologies due to the characters of extreme manufacturing in terms of size and quality requirements.This paper introduced a systematically method called cylinder unfolding method(CUM)for producing large plate forgings,by using a serial of operations including“splitting”,“unfolding”,and“flattening”of a thick cylinder obtained from saddle forging.The technological route of CUM was presented in detail with an example of plate forging with the horizontal sizes of 6100 mm and thickness of 300 mm.The deformation features of saddle forging for fabricating transitional cylinders were analyzed,and then the subsequent handling steps including splitting,unfolding and flattening of the cylinder,as well as the auxiliary processing,were addressed.The practice proved that CUM can provide an efficient way for manufacturing ultra-large plate forgings and meet the strict requirements in geometry and mechanical performance,without highly increasing the investments of forming equipment and tooling.展开更多
The folding and unfolding of the carbon chain,which is the basic constitutional unit of polymers,are important to the performance of the material.However,it is difficult to regulate conformational transition of the ca...The folding and unfolding of the carbon chain,which is the basic constitutional unit of polymers,are important to the performance of the material.However,it is difficult to regulate conformational transition of the carbon chain,especially in an aqueous environment.In this paper,we propose a strategy to regulate the conformational transition of the carbon chain in water based on the all-atom molecular dynamics simulations.It is shown that the unfolded carbon chain will spontaneously collapse into the folded state,while the folded carbon chain will unfold with an external electric field.The regulation ability of the electric field is attributed to the electric field-induced redistribution of interface water molecules near the carbon chain.The demonstrated method of regulating conformational transition of the carbon chain in water in this study provides an insight into regulating hydrophobic molecules in water,and has great potential in drug molecule design and new polymer material development.展开更多
Rate splitting multiple access(RSMA)has shown great potentials for the next generation communication systems.In this work,we consider a two-user system in hybrid satellite terrestrial network(HSTN)where one of them is...Rate splitting multiple access(RSMA)has shown great potentials for the next generation communication systems.In this work,we consider a two-user system in hybrid satellite terrestrial network(HSTN)where one of them is heavily shadowed and the other uses cooperative RSMA to improve the transmission quality.The non-convex weighted sum rate(WSR)problem formulated based on this model is usually optimized by computational burdened weighted minimum mean square error(WMMSE)algorithm.We propose to apply deep unfolding to solve the optimization problem,which maps WMMSE iterations into a layer-wise network and could achieve better performance within limited iterations.We also incorporate momentum accelerated projection gradient descent(PGD)algorithm to circumvent the complicated operations in WMMSE that are not amenable for unfolding and mapping.The momentum and step size in deep unfolding network are selected as trainable parameters for training.As shown in the simulation results,deep unfolding scheme has WSR and convergence speed advantages over original WMMSE algorithm.展开更多
We introduced stability of arbitrary degree number for unfordings of bifurcation problems and established the equivalence of three stabilities. Thom's transversality theory is used to character the new stability.
基金support by the National Key R&D Program of China(No.2022YFA1305200,to GL)National Natural Science Foundation of China(No.22104064 to GL,No.22173020 to JL)the US National Institute of Mental Health(No.R01MH122742,to CJW)for financial and instrumental support.
文摘Despite the expansive applications of gas-phase unfolding techniques,the molecular mechanism for the solvent-free forced unfolding pathway which substrate multidomain proteins usually adopt remains elusive at the secondary structure level.Herein,upon carefully selecting CRM_(197) as a therapeutically-relevant model system containing multiple secondary structure-separated domains,we systematically examine its solvent-free unfolding pathway.Further-more,utilizing the hybrid of noncovalent chemical probing with niacinamide and ion mobility-mass spectrometry-guided all-atom molecular dynamics simulations,we map a nearly complete unfolding atlas for the conjugate vaccine carrier protein CRM_(197) in a domain-and secondary structure-resolved manner.The totality of our data supports the preferential unfolding of the sheet-rich domain,indicating the dynamic transition from β-sheet toα-helix,and demonstrating that helix exhibit comparatively higher stability thanβ-sheets.We propose that this sheet-to-helix dynamic transition may be central to the gas-phase unfolding pathways of multidomain proteins,suggesting the need for systematic studies on additional multidomain protein systems.
基金supported by the National Natural Science Foun-dation of China(Grant Nos.12174322,12474200,32271367,and 12204389)111 Project(B16029)Research Grant from Wenzhou Institute.
文摘Spectrin domains,characterized by a distinctive triple helix structure,are crucial in physiological processes,particularly in maintaining membrane shape and crosslinking cytoskeletons.Previous research on the 16th domain of a-spectrin repeats(R16)has yielded conflicting results:bulk experiments showed an unfolding rate approximately two orders of magnitude faster than the zero-force result extrapolated from single-molecule force spectroscopy experiments using atomic force microscopy(AFM).To address this discrepancy,we investigated the folding and unfolding rates of R16 across a broader range of forces using magnetic tweezers(MT).Our findings reveal that AFM results at higher forces cannot be directly extrapolated to the low-force regime due to a nonlinear relationship between force and the logarithm of the unfolding rate.We demonstrated that two-dimensional model,structural-elastic model,and two-pathway model can all effectively explain the experimental data when they capture the core physics of the short unfolding distance at low forces.Our study provides a more comprehensive understanding of the unfolding dynamics of the spectrin domain,resolves previous contradictory experimental results,and highlights the common basis of different theoretical models.
文摘In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the relationship between the experimental and simulation results were explored.Our computational findings on the secondary structure of SEB showed that at room temperature,the CD spectroscopic results were highly consistent with the MD results.Moreover,under heating conditions,the changing trends of helix,sheet and random coil obtained by CD spectral fitting were highly consistent with those obtained by MD.In order to gain a deeper understanding of the thermal stability mechanism of SEB,the MD trajectories were analyzed in terms of root mean square deviation(RMSD),secondary structure assignment(SSA),radius of gyration(R_(g)),free energy surfaces(FES),solvent-accessible surface area(SASA),hydrogen bonds and salt bridges.The results showed that at low heating temperature,domain Ⅰ without loops(omitting the mobile loop region)mainly relied on hydrophobic interaction to maintain its thermal stability,whereas the thermal stability of domain Ⅱ was mainly controlled by salt bridges and hydrogen bonds.Under high heating temperature conditions,the hydrophobic interactions in domain Ⅰ without loops were destroyed and the secondary structure was almost completely lost,while domain Ⅱ could still rely on salt bridges as molecular staples to barely maintain the stability of the secondary structure.These results help us to understand the thermodynamic and kinetic mechanisms that maintain the thermal stability of SEB at the molecular level,and provide a direction for establishing safer and more effective food sterilization processes.
基金supported by the Korea Science and Engineering Foundation Grant(National Research Laboratory Program,R0A-2007-000-200012-0)the Korea Research Foundation(KRF-006-005-J03301)partially supported by the 2009 KU Brain Pool of Konkuk University
文摘In an attempt to realize a flapping wing micro-air vehicle with morphing wings, we report on improvements to our previousfoldable artificial hind wing.Multiple hinges, which were implemented to mimic the bending zone of a beetle hind wing, weremade of small composite hinge plates and tiny aluminum rivets.The buck-tails of rivets were flared after the hinge plates wereassembled with the rivets so that the folding/unfolding motions could be completed in less time, and the straight shape of theartificial hind wing could be maintained after fabrication.Folding and unfolding actions were triggered by electrically-activatedShape Memory Alloy (SMA) wires.For wing folding, the actuation characteristics of the SMA wire actuator were modifiedthrough heat treatment.Through a series of flapping tests, we confirmed that the artificial wings did not fold back and arbitrarilyfluctuate during the flapping motion.
基金supported by the National Key R&D Program of the MOST of China(No.2016YFA0300204)the National Natural Science Foundation of China(Nos.11227902)as part of the Si PáME2beamline project+1 种基金supported by the National Natural Science Foundation of China(No.41774120)the Sichuan Science and Technology Program(No.2021YJ0329)。
文摘A self-adaptive differential evolution neutron spectrum unfolding algorithm(SDENUA)is established in this study to unfold the neutron spectra obtained from a water-pumping-injection multilayered concentric sphere neutron spectrometer(WMNS).Specifically,the neutron fluence bounds are estimated to accelerate the algorithm convergence,and the minimum error between the optimal solution and input neutron counts with relative uncertainties is limited to 10^(-6)to avoid unnecessary calculations.Furthermore,the crossover probability and scaling factor are self-adaptively controlled.FLUKA Monte Carlo is used to simulate the readings of the WMNS under(1)a spectrum of Cf-252 and(2)its spectrum after being moderated,(3)a spectrum used for boron neutron capture therapy,and(4)a reactor spectrum.Subsequently,the measured neutron counts are unfolded using the SDENUA.The uncertainties of the measured neutron count and the response matrix are considered in the SDENUA,which does not require complex parameter tuning or an a priori default spectrum.The results indicate that the solutions of the SDENUA agree better with the IAEA spectra than those of MAXED and GRAVEL in UMG 3.1,and the errors of the final results calculated using the SDENUA are less than 12%.The established SDENUA can be used to unfold spectra from the WMNS.
基金Project supported by the National Science Foundation,China(No.61003099)the National Basic Research Program,China(No.2009CB320700)
文摘Determining the similarity degree between process models was very important for their management,reuse,and analysis.Current approaches either focused on process model's structural aspect,or had inefficiency or imprecision in behavioral similarity.Aiming at these problems,a novel similarity measure which extended an existing method named Transition Adjacent Relation(TAR) with improved precision and efficiency named TAR * was proposed.The ability of measuring similarity was extended by eliminating the duplicate tasks without impacting the behaviors.For precision,TARs was classified into repeatable and unrepeatable ones to identify whether a TAR was involved in a loop.Two new kinds of TARs were added,one related to the invisible tasks after the source place and before sink place,and the other representing implicit dependencies.For efficiency,all TARs based on unfolding instead of its reach ability graph of a labeled Petri net were calculated to avoid state space explosion.Experiments on artificial and real-world process models showed the effectiveness and efficiency of the proposed method.
基金supported by the State Key Development Program for Basic Research of China (Nos. 2008CB717803, 2009GB107001,2007CB209903)the Research Fund for the Doctoral Program of Higher Education of China (No. 200610011023)National Natural Science Foundation of China (No. 10875002)
文摘An accurate energy calibration of a 5＂× 2＂ BC501A liquid scintillator-based neutron detector by means of photon sources and the unfolding of pulse height spectra are described. The photon responses were measured with 22Na, 137Cs and 54Mn photon sources and simulated using the GRESP code, which was developed at the Physiknlisch Technische Bundesanstalt in Germany. Pulse height spectra produced by three different photon sources were employed to investigate the effects of the unfolding techniques. It was found that the four unfolding codes of the HEPRO and UMG3.3 packages, including GRAVEL, UNFANA, MIEKE and MAXED, performed well with the test spectra and produced generally consistent results. They could therefore be used to obtain neutron energy spectra in toknmak experiments.
基金Supported by the National Natural Science Foundation of China(10774115)the Doctoral Fund of Ministry of Education of China(20110141110009)
文摘Many biological functions of RNA molecules are re- lated to their pseudoknot structures. It is significant for predicting the structure and function of RNA that learning about the stability and the process of RNA pseudoknot folding and unfolding. The structural features of mouse mammary tumor virus （MMTV） RNA pseudoknot in different ion concentration, the unfolding process of the RNA pseudoknot, and the two hairpin helices that constitute the RNA pseudoknot were studied with all atom molecule dynam- ics simulation method in this paper. We found that the higher cation concentration can cause structure of the RNA molecules more stable, and ions played an indispensable role in keeping the structure of RNA molecules stable; the unfolding process of hair- pin structure was corresponding to the antiprocess of its folding process. The main pathway of pseudoknot unfolding was that the inner base pair opened first, and then, the two helices, which formed the RNA pseudoknot opened decussately, while the folding pathway of the RNA pseudoknot was a helix folding after forma- tion of the other helix. Therefore, the unfolding process of RNA pseudoknot is different from the antiprocess of its folding process, and the unfolding process of each helix in the RNA pseudoknot is similar to the hairpin structure＇s unfolding process, which means that both are the unzipping process.
基金supported by the National Natural science Foundation of China (No. 42127807)the Sichuan Science and Technology Program (No. 2020YJ0334)the Sichuan Science and Technology Breeding Program (No. 2022041)。
文摘The neutron spectrum unfolding by Bonner sphere spectrometer(BSS) is considered a complex multidimensional model,which requires complex mathematical methods to solve the first kind of Fredholm integral equation. In order to solve the problem of the maximum likelihood expectation maximization(MLEM) algorithm which is easy to suffer the pitfalls of local optima and the particle swarm optimization(PSO) algorithm which is easy to get unreasonable flight direction and step length of particles, which leads to the invalid iteration and affect efficiency and accuracy, an improved PSO-MLEM algorithm, combined of PSO and MLEM algorithm, is proposed for neutron spectrum unfolding. The dynamic acceleration factor is used to balance the ability of global and local search, and improves the convergence speed and accuracy of the algorithm. Firstly, the Monte Carlo method was used to simulated the BSS to obtain the response function and count rates of BSS. In the simulation of count rate, four reference spectra from the IAEA Technical Report Series No. 403 were used as input parameters of the Monte Carlo method. The PSO-MLEM algorithm was used to unfold the neutron spectrum of the simulated data and was verified by the difference of the unfolded spectrum to the reference spectrum. Finally, the 252Cf neutron source was measured by BSS, and the PSO-MLEM algorithm was used to unfold the experimental neutron spectrum.Compared with maximum entropy deconvolution(MAXED), PSO and MLEM algorithm, the PSO-MLEM algorithm has fewer parameters and automatically adjusts the dynamic acceleration factor to solve the problem of local optima. The convergence speed of the PSO-MLEM algorithm is 1.4 times and 3.1 times that of the MLEM and PSO algorithms. Compared with PSO, MLEM and MAXED, the correlation coefficients of PSO-MLEM algorithm are increased by 33.1%, 33.5% and 1.9%, and the relative mean errors are decreased by 98.2%, 97.8% and 67.4%.
基金the National Natural Science Foundation of China(Grant Nos.11874309 and 11474237)the 111 Project(Grant No.B16029)。
文摘Src SH3 protein domain is a typical two-state protein which has been confirmed by research of denaturant-induced unfolding dynamics.Force spectroscopy experiments by optical tweezers and atomic force microscopy have measured the force-dependent unfolding rates with different kinds of pulling geometry.However,the equilibrium folding and unfolding dynamics at constant forces has not been reported.Here,using stable magnetic tweezers,we performed equilibrium folding and unfolding dynamic measurement and force-jump measurement of src SH3 domain with tethering points at its N-and C-termini.From the obtained force-dependent transition rates,a detailed two-state free energy landscape of src SH3 protein is constructed with quantitative information of folding free energy,transition state barrier height and position,which exemplifies the capability of magnetic tweezers to study protein folding and unfolding dynamics.
基金This work was supported by the National Natural Science Foundation of China(Grants 11672268 and 91748209)the Fundamental Research Funds for Central Universities of China(Grant 2020XZZX005-02).
文摘To gain more understanding of cell-matrix adhesion,we consider an idealized theoretical model of a cluster of integrin-fibronectin bonds at the cell-matrix interface subjected to a dynamic ramping.The distributions of bond traction and interfacial deformation are assumed to obey classical elastic equations,whereas the dissociation/association of individual bonds as well as unfolding/refolding of fibronectin domains are described by stochastic equations.Through stochastic-elasticity coupling,we perform Monte Carlo simulations to investigate how the collective behavior and adhesion performance of the integrin-fibronectin-mediated interface are influenced by two characteristics newly incorporated in the modeling,i.e.,catchlike dissociation between integrin and fibronectin,and unfolding of repeated domains in fibronectin.The probable unfolding of fibronectin domains is found to have profound effects on the resultant adhesion energy of the integrin-fibronectin-mediated interface,and governs the failure model transiting between uniform decay and catastrophic crack-like rupture.
基金Supported by the National Nature Science Foundation of China (10261002)
文摘In this paper,the (?)-equivariant (s, t)-equivalence relation and (?)-equivariant infinitesimally (r, s)-stability of (?)-equivariant bifurcation problem are defined. The criterion for (?)-equivariant infinitesimally (r, s)-stability is proven when (?) is a compact finite Lie group .Transversality condition is used to characterize the stability.
文摘For the unfolding of equivariant bifurcation problems with two types of state variables in the presence of parameter symmetry,the versal unfolding theorem with respect to left-right equivalence is obtained by using the related methods and techniques in the singularity theory of smooth map-germs.The corresponding results in[4,9]can be considered as its special cases.A relationship between the versal unfolding w.r.t.left-right equivalence and the versal deformation w.r.t.contact equivalence is established.
基金Project(cstc2018jcyjAX0159)supported by the Natural Science Foundation of Chongqing,ChinaProject(51575066)supported by the National Natural Science Foundation of China。
文摘Ultra-large plate forgings are foundation of heavy machinery,but many parts of the type cannot be made by conventional technologies due to the characters of extreme manufacturing in terms of size and quality requirements.This paper introduced a systematically method called cylinder unfolding method(CUM)for producing large plate forgings,by using a serial of operations including“splitting”,“unfolding”,and“flattening”of a thick cylinder obtained from saddle forging.The technological route of CUM was presented in detail with an example of plate forging with the horizontal sizes of 6100 mm and thickness of 300 mm.The deformation features of saddle forging for fabricating transitional cylinders were analyzed,and then the subsequent handling steps including splitting,unfolding and flattening of the cylinder,as well as the auxiliary processing,were addressed.The practice proved that CUM can provide an efficient way for manufacturing ultra-large plate forgings and meet the strict requirements in geometry and mechanical performance,without highly increasing the investments of forming equipment and tooling.
基金This work was partially supported by the Zhejiang Provincial Natural Science Foundation of China(No.LR21A020001)the National Natural Science Foundation of China(No.11774313).J.K.was supported by the Start-up fund of Zhejiang Normal University.
文摘The folding and unfolding of the carbon chain,which is the basic constitutional unit of polymers,are important to the performance of the material.However,it is difficult to regulate conformational transition of the carbon chain,especially in an aqueous environment.In this paper,we propose a strategy to regulate the conformational transition of the carbon chain in water based on the all-atom molecular dynamics simulations.It is shown that the unfolded carbon chain will spontaneously collapse into the folded state,while the folded carbon chain will unfold with an external electric field.The regulation ability of the electric field is attributed to the electric field-induced redistribution of interface water molecules near the carbon chain.The demonstrated method of regulating conformational transition of the carbon chain in water in this study provides an insight into regulating hydrophobic molecules in water,and has great potential in drug molecule design and new polymer material development.
基金sponsored by National Natural Science Foundation of China (No. 61871422, No.62027801)
文摘Rate splitting multiple access(RSMA)has shown great potentials for the next generation communication systems.In this work,we consider a two-user system in hybrid satellite terrestrial network(HSTN)where one of them is heavily shadowed and the other uses cooperative RSMA to improve the transmission quality.The non-convex weighted sum rate(WSR)problem formulated based on this model is usually optimized by computational burdened weighted minimum mean square error(WMMSE)algorithm.We propose to apply deep unfolding to solve the optimization problem,which maps WMMSE iterations into a layer-wise network and could achieve better performance within limited iterations.We also incorporate momentum accelerated projection gradient descent(PGD)algorithm to circumvent the complicated operations in WMMSE that are not amenable for unfolding and mapping.The momentum and step size in deep unfolding network are selected as trainable parameters for training.As shown in the simulation results,deep unfolding scheme has WSR and convergence speed advantages over original WMMSE algorithm.
基金Supported by the National Natural Science Foundation of China(198710 74)
文摘We introduced stability of arbitrary degree number for unfordings of bifurcation problems and established the equivalence of three stabilities. Thom's transversality theory is used to character the new stability.
