We investigated the parametric optimization on incremental sheet forming of stainless steel using Grey Relational Analysis(GRA) coupled with Principal Component Analysis(PCA). AISI 316L stainless steel sheets were use...We investigated the parametric optimization on incremental sheet forming of stainless steel using Grey Relational Analysis(GRA) coupled with Principal Component Analysis(PCA). AISI 316L stainless steel sheets were used to develop double wall angle pyramid with aid of tungsten carbide tool. GRA coupled with PCA was used to plan the experiment conditions. Control factors such as Tool Diameter(TD), Step Depth(SD), Bottom Wall Angle(BWA), Feed Rate(FR) and Spindle Speed(SS) on Top Wall Angle(TWA) and Top Wall Angle Surface Roughness(TWASR) have been studied. Wall angle increases with increasing tool diameter due to large contact area between tool and workpiece. As the step depth, feed rate and spindle speed increase,TWASR decreases with increasing tool diameter. As the step depth increasing, the hydrostatic stress is raised causing severe cracks in the deformed surface. Hence it was concluded that the proposed hybrid method was suitable for optimizing the factors and response.展开更多
Single point diamond fly cutting is widely used in the manufacture of large-aperture ultra-precision optical elements. However,some micro waviness( amplitude about 30 nm,wavelength about 15 mm) along the cutting direc...Single point diamond fly cutting is widely used in the manufacture of large-aperture ultra-precision optical elements. However,some micro waviness( amplitude about 30 nm,wavelength about 15 mm) along the cutting direction which will decrease the quality of the optical elements can always be found in the processed surface,and the axial vibration of the spindle caused by the cut-in process is speculated as the immediate cause of this waviness. In this paper,the analytical method of dynamic mesh is applied for simulating the dynamic behavior of the vertical spindle. The consequence is then exerted to the fly cutter and the processed surface profile is simulated. The wavelength of the simulation result coincides well with the experimental result which proves the importance of the cut-in process during the single point diamond fly cutting.展开更多
By friction heating single point incremental forming,truncated square pyramid parts with different draw angles of a magnesium alloy AZ31 B were formed at room temperature.Metallurgical,tensile and micro-hardness tests...By friction heating single point incremental forming,truncated square pyramid parts with different draw angles of a magnesium alloy AZ31 B were formed at room temperature.Metallurgical,tensile and micro-hardness tests were carried out to obtain the effects of wall angle on microstructure and mechanical properties. The results show that grain in side wall of the formed parts becomes refined significantly. Furthermore,with the increase of draw angle,grain size increases,but strength,hardness and plasticity decrease. In addition, surface roughness tests were performed on the formed surface to determine the influence of speed of forming tool. The results show that surface roughness has a little increase with the increase of tool rotational speed.展开更多
To effectively solve the problems of inconsistent communication protocols in automatic monitoring equipment,and limited data acquisition transmission and monitoring equipment,this paper developed programmable single p...To effectively solve the problems of inconsistent communication protocols in automatic monitoring equipment,and limited data acquisition transmission and monitoring equipment,this paper developed programmable single point multiple output intelligent data acquisition and transmission system. It made an in-depth elaboration of the data acquisition and transmission system from hardware design,software architecture and principle,main functions and technical parameters. Finally,it came up with four innovation points:(i) intelligent(automatic)matching a variety of communication protocols for environmental monitoring equipment,(ii) realizing multi-protocol and multi-target parallel data transmission,(iii) realizing remote dynamic input of control instructions through wired or wireless network,and(iv) supporting configuration(process) simulation of field equipment DCS operating conditions.展开更多
Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM...Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM)strategy to suppress the ZSC.Five vectors are selected as basic voltage vectors in one switching period.The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector.To suppress the ZSC,a non-zero zero-sequence voltage(ZSV)is generated to compensate the third harmonic back-EMF.Rather than triangular carrier modulation,the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals.The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane.With the proposed method,the ZSC can be considerably reduced.The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.展开更多
For the last two decades,low-cost Global Navigation Satellite System(GNSS)receivers have been used in various applications.These receivers are mini-size,less expensive than geodetic-grade receivers,and in high demand....For the last two decades,low-cost Global Navigation Satellite System(GNSS)receivers have been used in various applications.These receivers are mini-size,less expensive than geodetic-grade receivers,and in high demand.Irrespective of these outstanding features,low-cost GNSS receivers are potentially poorer hardwares with internal signal processing,resulting in lower quality.They typically come with low-cost GNSS antenna that has lower performance than their counterparts,particularly for multipath mitigation.Therefore,this research evaluated the low-cost GNSS device performance using a high-rate kinematic survey.For this purpose,these receivers were assembled with an Inertial Measurement Unit(IMU)sensor,which actively transmited data on acceleration and orientation rate during the observation.The position and navigation parameter data were obtained from the IMU readings,even without GNSS signals via the U-blox F9R GNSS/IMU device mounted on a vehicle.This research was conducted in an area with demanding conditions,such as an open sky area,an urban environment,and a shopping mall basement,to examine the device’s performance.The data were processed by two approaches:the Single Point Positioning-IMU(SPP/IMU)and the Differential GNSS-IMU(DGNSS/IMU).The Unscented Kalman Filter(UKF)was selected as a filtering algorithm due to its excellent performance in handling nonlinear system models.The result showed that integrating GNSS/IMU in SPP processing mode could increase the accuracy in eastward and northward components up to 68.28%and 66.64%.Integration of DGNSS/IMU increased the accuracy in eastward and northward components to 93.02%and 93.03%compared to the positioning of standalone GNSS.In addition,the positioning accuracy can be improved by reducing the IMU noise using low-pass and high-pass filters.This application could still not gain the expected position accuracy under signal outage conditions.展开更多
Time series data is a kind of data accumulated over time,which can describe the change of phenomenon.This kind of data reflects the degree of change of a certain thing or phenomenon.The existing technologies such as L...Time series data is a kind of data accumulated over time,which can describe the change of phenomenon.This kind of data reflects the degree of change of a certain thing or phenomenon.The existing technologies such as LSTM and ARIMA are better than convolutional neural network in time series prediction,but they are not enough to mine the periodicity of data.In this article,we perform periodic analysis on two types of time series data,select time metrics with high periodic characteristics,and propose a multi-scale prediction model based on the attention mechanism for the periodic trend of the data.A loss calculation method for traffic time series characteristics is proposed as well.Multiple experiments have been conducted on actual data sets.The experiments show that the method proposed in this paper has better performance than commonly used traffic prediction methods(ARIMA,LSTM,etc.)and 3%-5%increase on MAPE.展开更多
As a critical Internet infrastructure,domain name system(DNS)protects the authenticity and integrity of domain resource records with the introduction of security extensions(DNSSEC).DNSSEC builds a single-center and hi...As a critical Internet infrastructure,domain name system(DNS)protects the authenticity and integrity of domain resource records with the introduction of security extensions(DNSSEC).DNSSEC builds a single-center and hierarchical resource authentication architecture,which brings management convenience but places the DNS at risk from a single point of failure.When the root key suffers a leak or misconfiguration,top level domain(TLD)authority cannot independently protect the authenticity of TLD data in the root zone.In this paper,we propose self-certificating root,a lightweight security enhancement mechanism of root zone compatible with DNS/DNSSEC protocol.By adding the TLD public key and signature of the glue records to the root zone,this mechanism enables the TLD authority to certify the self-submitted data in the root zone and protects the TLD authority from the risk of root key failure.This mechanism is implemented on an open-source software,namely,Berkeley Internet Name Domain(BIND),and evaluated in terms of performance,compatibility,and effectiveness.Evaluation results show that the proposed mechanism enables the resolver that only supports DNS/DNSSEC to authenticate the root zone TLD data effectively with minimal performance difference.展开更多
Calculating the absolute open flow potential timely and investigating production capacity so as to adjust working system of production wells is one of main means to effectively recovery gas reservoirs during intermedi...Calculating the absolute open flow potential timely and investigating production capacity so as to adjust working system of production wells is one of main means to effectively recovery gas reservoirs during intermediate and late development stage.In order to obtain the open flow potential of gas wells accurately,a new method which utilized a single steady point was proposed in this research,which was based on deliverability formula of a gas well in pseudo-steady state flow with pseudo-pressure form.The influence on factor B in binomial productivity equation caused by the changed permeability was taken into consideration.According to the stable production data,reservoir permeability K can be determined by iterative method firstly,and the coefficient A,B in binomial productivity equation can be calculated with the open flow potential subsequently.It illustrated clearly by a practical example that the new method was suitable for gas wells especially when the producing pressure drop is large.Additionally,the error between the open flow potential value and interpretation result from the multi-point test was small,which proved it to be more simple,economic and effective than the common one.展开更多
Identity-based threshold signature(IDTS)is a forceful primitive to protect identity and data privacy,in which parties can collaboratively sign a given message as a signer without reconstructing a signing key.Neverthel...Identity-based threshold signature(IDTS)is a forceful primitive to protect identity and data privacy,in which parties can collaboratively sign a given message as a signer without reconstructing a signing key.Nevertheless,most IDTS schemes rely on a trusted key generation center(KGC).Recently,some IDTS schemes can achieve escrow-free security against corrupted KGC,but all of them are vulnerable to denial-of-service attacks in the dishonest majority setting,where cheaters may force the protocol to abort without providing any feedback.In this work,we present a fully decentralized IDTS scheme to resist corrupted KGC and denialof-service attacks.To this end,we design threshold protocols to achieve distributed key generation,private key extraction,and signing generation which can withstand the collusion between KGCs and signers,and then we propose an identification mechanism that can detect the identity of cheaters during key generation,private key extraction and signing generation.Finally,we formally prove that the proposed scheme is threshold unforgeability against chosen message attacks.The experimental results show that the computation time of both key generation and signing generation is<1 s,and private key extraction is about 3 s,which is practical in the distributed environment.展开更多
A long-term analysis of signal-in-space range error (SISRE) is presented for all healthy Galileo satellites, and the first pair of full operational capability satellites in wrong elliptical orbits. Both orbit and cloc...A long-term analysis of signal-in-space range error (SISRE) is presented for all healthy Galileo satellites, and the first pair of full operational capability satellites in wrong elliptical orbits. Both orbit and clock errors for Galileo show an obvious convergence trend over time. The annual statistical analyses show that the average root mean squares (RMSs) of SISRE for the Galileo constellation are 0.58 m (2015), 0.29 m (2016), 0.23 m (2017), and 0.22 m (2018). Currently, the accuracy of the Galileo signal-in-space is superior to that of the global positioning system (GPS) Block IIF (0.35 m). In addition, the orbit error accounts for the majority of Galileo SISRE, while the clock error accounts for approximately one-third of SISRE due to the high stability of the onboard atomic clock. Single point positioning results show that Galileo achieves an accuracy of 2-3 m, which is comparable to that of GPS despite the smaller number of satellites and worse geometry. Interestingly, the vertical accuracy of Galileo, which uses the NeQuick ionospheric model, is higher than that of GPS. Positioning with single frequency E1 and E5 show a higher precision than E5a and E5b signals. Regarding precise point positioning (PPP), the results indicate that a comparable positioning accuracy can be achieved among different stations with the current Galileo constellation. For static PPP, the RMS values of Galileo-only solutions are within 1 cm horizontally, and the vertical RMSs are mostly within 2 cm horizontally. For kinematic PPP, the RMSs of Galileo-only solutions are mostly within 4 cm horizontally and 6 cm vertically.展开更多
Many molecular events are associated with small or large conformational changes occurring in the corresponding proteins.Modeling such changes is a challenge and requires significant amount of computing time.From point...Many molecular events are associated with small or large conformational changes occurring in the corresponding proteins.Modeling such changes is a challenge and requires significant amount of computing time.From point of view of electrostatics,these changes can be viewed as a reorganization of local charges and dipoles in response to the changes of the electrostatic field,if the cause is insertion or deletion of a charged amino acid.Here we report a large scale investigation of modeling the changes of the folding energy due to single mutations involving charged group.This allows the changes of the folding energy to be considered mostly electrostatics in origin and to be calculated with DelPhi assigning residue-specific value of the internal dielectric constant of protein.The predicted energy changes are benchmarked against experimentally measured changes of the folding energy on a set of 257 single mutations.The best fit between experimental values and predicted changes is used to find out the effective value of the internal dielectric constant for each type of amino acid.The predicted folding free energy changes with the optimal,amino acid specific,dielectric constants are within RMSD=0.86 kcal/mol from experimentally measured changes.展开更多
文摘We investigated the parametric optimization on incremental sheet forming of stainless steel using Grey Relational Analysis(GRA) coupled with Principal Component Analysis(PCA). AISI 316L stainless steel sheets were used to develop double wall angle pyramid with aid of tungsten carbide tool. GRA coupled with PCA was used to plan the experiment conditions. Control factors such as Tool Diameter(TD), Step Depth(SD), Bottom Wall Angle(BWA), Feed Rate(FR) and Spindle Speed(SS) on Top Wall Angle(TWA) and Top Wall Angle Surface Roughness(TWASR) have been studied. Wall angle increases with increasing tool diameter due to large contact area between tool and workpiece. As the step depth, feed rate and spindle speed increase,TWASR decreases with increasing tool diameter. As the step depth increasing, the hydrostatic stress is raised causing severe cracks in the deformed surface. Hence it was concluded that the proposed hybrid method was suitable for optimizing the factors and response.
基金Sponsored by the National Science and Technology Special Program(Grant No.2011ZX04004-041)the National Natural Science Foundation of China(Grant No.90923023 and No.51275115)
文摘Single point diamond fly cutting is widely used in the manufacture of large-aperture ultra-precision optical elements. However,some micro waviness( amplitude about 30 nm,wavelength about 15 mm) along the cutting direction which will decrease the quality of the optical elements can always be found in the processed surface,and the axial vibration of the spindle caused by the cut-in process is speculated as the immediate cause of this waviness. In this paper,the analytical method of dynamic mesh is applied for simulating the dynamic behavior of the vertical spindle. The consequence is then exerted to the fly cutter and the processed surface profile is simulated. The wavelength of the simulation result coincides well with the experimental result which proves the importance of the cut-in process during the single point diamond fly cutting.
基金National Natural Science Foundation of China(No.51205217)
文摘By friction heating single point incremental forming,truncated square pyramid parts with different draw angles of a magnesium alloy AZ31 B were formed at room temperature.Metallurgical,tensile and micro-hardness tests were carried out to obtain the effects of wall angle on microstructure and mechanical properties. The results show that grain in side wall of the formed parts becomes refined significantly. Furthermore,with the increase of draw angle,grain size increases,but strength,hardness and plasticity decrease. In addition, surface roughness tests were performed on the formed surface to determine the influence of speed of forming tool. The results show that surface roughness has a little increase with the increase of tool rotational speed.
文摘To effectively solve the problems of inconsistent communication protocols in automatic monitoring equipment,and limited data acquisition transmission and monitoring equipment,this paper developed programmable single point multiple output intelligent data acquisition and transmission system. It made an in-depth elaboration of the data acquisition and transmission system from hardware design,software architecture and principle,main functions and technical parameters. Finally,it came up with four innovation points:(i) intelligent(automatic)matching a variety of communication protocols for environmental monitoring equipment,(ii) realizing multi-protocol and multi-target parallel data transmission,(iii) realizing remote dynamic input of control instructions through wired or wireless network,and(iv) supporting configuration(process) simulation of field equipment DCS operating conditions.
基金supported in part by the National Natural Science Foundation of China under Grant 51977099。
文摘Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM)strategy to suppress the ZSC.Five vectors are selected as basic voltage vectors in one switching period.The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector.To suppress the ZSC,a non-zero zero-sequence voltage(ZSV)is generated to compensate the third harmonic back-EMF.Rather than triangular carrier modulation,the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals.The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane.With the proposed method,the ZSC can be considerably reduced.The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.
基金funded by the project scheme of the Publication Writing-IPR Incentive Program(PPHKI)2022Directorate of Research and Community Service(DRPM)Institut Teknologi Sepuluh Nopember(ITS)Surabaya,Indonesia for the financial supports。
文摘For the last two decades,low-cost Global Navigation Satellite System(GNSS)receivers have been used in various applications.These receivers are mini-size,less expensive than geodetic-grade receivers,and in high demand.Irrespective of these outstanding features,low-cost GNSS receivers are potentially poorer hardwares with internal signal processing,resulting in lower quality.They typically come with low-cost GNSS antenna that has lower performance than their counterparts,particularly for multipath mitigation.Therefore,this research evaluated the low-cost GNSS device performance using a high-rate kinematic survey.For this purpose,these receivers were assembled with an Inertial Measurement Unit(IMU)sensor,which actively transmited data on acceleration and orientation rate during the observation.The position and navigation parameter data were obtained from the IMU readings,even without GNSS signals via the U-blox F9R GNSS/IMU device mounted on a vehicle.This research was conducted in an area with demanding conditions,such as an open sky area,an urban environment,and a shopping mall basement,to examine the device’s performance.The data were processed by two approaches:the Single Point Positioning-IMU(SPP/IMU)and the Differential GNSS-IMU(DGNSS/IMU).The Unscented Kalman Filter(UKF)was selected as a filtering algorithm due to its excellent performance in handling nonlinear system models.The result showed that integrating GNSS/IMU in SPP processing mode could increase the accuracy in eastward and northward components up to 68.28%and 66.64%.Integration of DGNSS/IMU increased the accuracy in eastward and northward components to 93.02%and 93.03%compared to the positioning of standalone GNSS.In addition,the positioning accuracy can be improved by reducing the IMU noise using low-pass and high-pass filters.This application could still not gain the expected position accuracy under signal outage conditions.
基金This work is supported by the National Natural Science Foundation of China(Grant No.61971057)MoE-CMCC Artifical Intelligence Project(No.MCM20190701).
文摘Time series data is a kind of data accumulated over time,which can describe the change of phenomenon.This kind of data reflects the degree of change of a certain thing or phenomenon.The existing technologies such as LSTM and ARIMA are better than convolutional neural network in time series prediction,but they are not enough to mine the periodicity of data.In this article,we perform periodic analysis on two types of time series data,select time metrics with high periodic characteristics,and propose a multi-scale prediction model based on the attention mechanism for the periodic trend of the data.A loss calculation method for traffic time series characteristics is proposed as well.Multiple experiments have been conducted on actual data sets.The experiments show that the method proposed in this paper has better performance than commonly used traffic prediction methods(ARIMA,LSTM,etc.)and 3%-5%increase on MAPE.
基金This work is partially supported by the National Key Research and Development Program(2018YFB1800702).
文摘As a critical Internet infrastructure,domain name system(DNS)protects the authenticity and integrity of domain resource records with the introduction of security extensions(DNSSEC).DNSSEC builds a single-center and hierarchical resource authentication architecture,which brings management convenience but places the DNS at risk from a single point of failure.When the root key suffers a leak or misconfiguration,top level domain(TLD)authority cannot independently protect the authenticity of TLD data in the root zone.In this paper,we propose self-certificating root,a lightweight security enhancement mechanism of root zone compatible with DNS/DNSSEC protocol.By adding the TLD public key and signature of the glue records to the root zone,this mechanism enables the TLD authority to certify the self-submitted data in the root zone and protects the TLD authority from the risk of root key failure.This mechanism is implemented on an open-source software,namely,Berkeley Internet Name Domain(BIND),and evaluated in terms of performance,compatibility,and effectiveness.Evaluation results show that the proposed mechanism enables the resolver that only supports DNS/DNSSEC to authenticate the root zone TLD data effectively with minimal performance difference.
基金Fund project:National Basic Research Program of China(973 Program-2014CB239205).
文摘Calculating the absolute open flow potential timely and investigating production capacity so as to adjust working system of production wells is one of main means to effectively recovery gas reservoirs during intermediate and late development stage.In order to obtain the open flow potential of gas wells accurately,a new method which utilized a single steady point was proposed in this research,which was based on deliverability formula of a gas well in pseudo-steady state flow with pseudo-pressure form.The influence on factor B in binomial productivity equation caused by the changed permeability was taken into consideration.According to the stable production data,reservoir permeability K can be determined by iterative method firstly,and the coefficient A,B in binomial productivity equation can be calculated with the open flow potential subsequently.It illustrated clearly by a practical example that the new method was suitable for gas wells especially when the producing pressure drop is large.Additionally,the error between the open flow potential value and interpretation result from the multi-point test was small,which proved it to be more simple,economic and effective than the common one.
基金support by the National Key R&D Program of China(No.2021YFB3100400)the National Natural Science Foundation of China(Grant Nos.62172216,U20A201092)+6 种基金the Jiangsu Provincial Key Research and Development Program(Nos.BE2022068,BE2022068-2)the Key R&D Program of Guangdong Province(No.2020B0101090002)the Natural Science Foundation of Jiangsu Province(No.BK20211180)the Research Fund of Guangxi Key Laboratory of Trusted Software(No.KX202034)the Research Fund of State Key Laboratory of Integrated Services Networks(Xidian University)(No.ISN23-20)the Fund of Prospective Layout of Scientific Research for NUAA(Nanjing University of Aeronautics and Astronautics)JSPS Postdoctoral Fellowships(No.P21073).
文摘Identity-based threshold signature(IDTS)is a forceful primitive to protect identity and data privacy,in which parties can collaboratively sign a given message as a signer without reconstructing a signing key.Nevertheless,most IDTS schemes rely on a trusted key generation center(KGC).Recently,some IDTS schemes can achieve escrow-free security against corrupted KGC,but all of them are vulnerable to denial-of-service attacks in the dishonest majority setting,where cheaters may force the protocol to abort without providing any feedback.In this work,we present a fully decentralized IDTS scheme to resist corrupted KGC and denialof-service attacks.To this end,we design threshold protocols to achieve distributed key generation,private key extraction,and signing generation which can withstand the collusion between KGCs and signers,and then we propose an identification mechanism that can detect the identity of cheaters during key generation,private key extraction and signing generation.Finally,we formally prove that the proposed scheme is threshold unforgeability against chosen message attacks.The experimental results show that the computation time of both key generation and signing generation is<1 s,and private key extraction is about 3 s,which is practical in the distributed environment.
基金the National Natural Science Foundation of China(No.41774034)the National Key Research and Development Program of China(No.2016YFB0501803,No.2017YFB0503402).
文摘A long-term analysis of signal-in-space range error (SISRE) is presented for all healthy Galileo satellites, and the first pair of full operational capability satellites in wrong elliptical orbits. Both orbit and clock errors for Galileo show an obvious convergence trend over time. The annual statistical analyses show that the average root mean squares (RMSs) of SISRE for the Galileo constellation are 0.58 m (2015), 0.29 m (2016), 0.23 m (2017), and 0.22 m (2018). Currently, the accuracy of the Galileo signal-in-space is superior to that of the global positioning system (GPS) Block IIF (0.35 m). In addition, the orbit error accounts for the majority of Galileo SISRE, while the clock error accounts for approximately one-third of SISRE due to the high stability of the onboard atomic clock. Single point positioning results show that Galileo achieves an accuracy of 2-3 m, which is comparable to that of GPS despite the smaller number of satellites and worse geometry. Interestingly, the vertical accuracy of Galileo, which uses the NeQuick ionospheric model, is higher than that of GPS. Positioning with single frequency E1 and E5 show a higher precision than E5a and E5b signals. Regarding precise point positioning (PPP), the results indicate that a comparable positioning accuracy can be achieved among different stations with the current Galileo constellation. For static PPP, the RMS values of Galileo-only solutions are within 1 cm horizontally, and the vertical RMSs are mostly within 2 cm horizontally. For kinematic PPP, the RMSs of Galileo-only solutions are mostly within 4 cm horizontally and 6 cm vertically.
基金supported by a grant from the Institute of General Medical Sciences,National Institutes of Health,award number 1R01GM093937-01.
文摘Many molecular events are associated with small or large conformational changes occurring in the corresponding proteins.Modeling such changes is a challenge and requires significant amount of computing time.From point of view of electrostatics,these changes can be viewed as a reorganization of local charges and dipoles in response to the changes of the electrostatic field,if the cause is insertion or deletion of a charged amino acid.Here we report a large scale investigation of modeling the changes of the folding energy due to single mutations involving charged group.This allows the changes of the folding energy to be considered mostly electrostatics in origin and to be calculated with DelPhi assigning residue-specific value of the internal dielectric constant of protein.The predicted energy changes are benchmarked against experimentally measured changes of the folding energy on a set of 257 single mutations.The best fit between experimental values and predicted changes is used to find out the effective value of the internal dielectric constant for each type of amino acid.The predicted folding free energy changes with the optimal,amino acid specific,dielectric constants are within RMSD=0.86 kcal/mol from experimentally measured changes.
