The three dimensional variable cross-section roll forming is a kind of new metal forming technol- ogy which combines large forming force, multi-axis linkage movement and space synergic movement, and the sequential syn...The three dimensional variable cross-section roll forming is a kind of new metal forming technol- ogy which combines large forming force, multi-axis linkage movement and space synergic movement, and the sequential synergic movement of the ganged roller group is used to complete the metal sheet forming according to the shape of the complicated and variable forming part data. The control system should meet the demands of quick response to the test requirements of the product part. A new kind of real time data driving multi-axis linkage and synergic movement control strategy of 3D roll forming is put forward in the paper. In the new control strategy, the forming data are automatically generated according to the shape of the parts, and the multi-axis linkage movement together with cooperative motion among the six stands of the 3D roll forming machine is driven by the real-time information, and the control nodes are also driven by the forming data. The new control strategy is applied to a 48 axis 3D roll forming machine developed by our research center, and the control servo period is less than 10ms. A forming experiment of variable cross section part is carried out, and the forming preci- sion is better than ＋ 0.5mm by the control strategy. The result of the experiment proves that the control strategy has significant potentiality for the development of 3D roll forming production line with large scale, multi-axis ganged and svner^ic movement展开更多
The simplified incidence function model which is driven by the colored correlated noises is employed to investigate the extinction time of a metapopulation perturbed by environments. The approximate Fokker-Planck Equa...The simplified incidence function model which is driven by the colored correlated noises is employed to investigate the extinction time of a metapopulation perturbed by environments. The approximate Fokker-Planck Equation and the mean first passage time which denotes the extinction time （Tex） are obtained by virtue of the Novikov theorem and the Fox approach. After introducing a noise intensity ratio and a dimensionless parameter R = D /α （D and a are the multiplicative and additive colored noise intensities respectively）, and then performing numerical computations, the results indicate that： （i） The absolute value of correlation strength A and its correlation time τ3 play opposite roles on the Tex; （ii） For the case of 0 〈λ〈 1,α and its correlation time τ2 play opposite roles on the Tex in which R〉 1 is the best condition, and there is one-peak structure on the Tex - D plot; （iii） For the case of-1 〈 λ≤ 0, D and its correlation time τ1 play opposite roles on the Tex in which R 〈 1 is the best condition and there is one-peak structure on the Tex - τ2 plot.展开更多
Molecular dynamics with the stochastic process provides a convenient way to compute structural and thermodynamic properties of chemical, biological, and materials systems. It is demonstrated that the virtual dynamics ...Molecular dynamics with the stochastic process provides a convenient way to compute structural and thermodynamic properties of chemical, biological, and materials systems. It is demonstrated that the virtual dynamics case that we proposed for the Langevin equation [J. Chem. Phys. 147, 184104 （2017）] in principle exists in other types of stochastic thermostats as well. The recommended ＂middle＂ scheme [J. Chem. Phys. 147, 034109 （2017）] of the Andersen thermostat is investigated as an example. As shown by both analytic and numerical results, while the real and virtual dynamics cases approach the same plateau of the characteristic correlation time in the high collision frequency limit, the accuracy and efficiency of sampling are relatively insensitive to the value of the collision frequency in a broad range. After we compare the behaviors of the Andersen thermostat to those of Langevin dynamics, a heuristic schematic representation thermostatting processes with molecular is proposed for understanding efficient stochastic dynamics.展开更多
Supported by a new generation of mobile devices, e-commerce is now in the process of being converted into m-commerce. While the traditional fixed PC access to the Internet continues to be important, the mobile access ...Supported by a new generation of mobile devices, e-commerce is now in the process of being converted into m-commerce. While the traditional fixed PC access to the Internet continues to be important, the mobile access appears to attract more people because of its flexibility. The purpose of this paper is to develop and analyze a mathematical model for capturing how e-commerce performance would be affected by the mobile access to the Internet, where the original paper by Sumita and Yoshii （2010） is extended for better reality. The traditional e-commerce via the fixed PC access is compared with m-commerce which accommodates both the fixed PC access and the mobile access. The distribution of the number of products purchased by time t and the distribution of the time required for selling K products are derived explicitly. Numerical examples are given for illustrating behavioral differences between m-commerce consumers and traditional e-commerce consumers.展开更多
In the design and construction process of Next Generation Internet, it is important to identify the source of each IP packet forwarding accurately, especially for the support of precise fine-grained management,control...In the design and construction process of Next Generation Internet, it is important to identify the source of each IP packet forwarding accurately, especially for the support of precise fine-grained management,control, traceability and improving the trustworthiness of the Internet. This paper designed a scalable Network Identity(NID) scheme for the Internet users, proposed NIDTGA(Network Identity and Time Generated Address), an IPv6 address generation algorithm embedded NID and time information, then designed and implemented an IPv6 address generation and traceback system based on NIDTGA. The design of NIDTGA, which reflects the length, time and owner attributes of the IP address, can be a good support to ADN(Address Driven Network). At the same time, by embedding the key elements of user identity and time in the IPv6 address,and by taking into account both the traceability and privacy, NIDTGA can provide a technical basis for the establishment of the network trust mechanism, and achieve the traceability of security event.展开更多
基金Supported by National Key Technology R&D Program(No.2011BAG03B03)
文摘The three dimensional variable cross-section roll forming is a kind of new metal forming technol- ogy which combines large forming force, multi-axis linkage movement and space synergic movement, and the sequential synergic movement of the ganged roller group is used to complete the metal sheet forming according to the shape of the complicated and variable forming part data. The control system should meet the demands of quick response to the test requirements of the product part. A new kind of real time data driving multi-axis linkage and synergic movement control strategy of 3D roll forming is put forward in the paper. In the new control strategy, the forming data are automatically generated according to the shape of the parts, and the multi-axis linkage movement together with cooperative motion among the six stands of the 3D roll forming machine is driven by the real-time information, and the control nodes are also driven by the forming data. The new control strategy is applied to a 48 axis 3D roll forming machine developed by our research center, and the control servo period is less than 10ms. A forming experiment of variable cross section part is carried out, and the forming preci- sion is better than ＋ 0.5mm by the control strategy. The result of the experiment proves that the control strategy has significant potentiality for the development of 3D roll forming production line with large scale, multi-axis ganged and svner^ic movement
文摘The simplified incidence function model which is driven by the colored correlated noises is employed to investigate the extinction time of a metapopulation perturbed by environments. The approximate Fokker-Planck Equation and the mean first passage time which denotes the extinction time （Tex） are obtained by virtue of the Novikov theorem and the Fox approach. After introducing a noise intensity ratio and a dimensionless parameter R = D /α （D and a are the multiplicative and additive colored noise intensities respectively）, and then performing numerical computations, the results indicate that： （i） The absolute value of correlation strength A and its correlation time τ3 play opposite roles on the Tex; （ii） For the case of 0 〈λ〈 1,α and its correlation time τ2 play opposite roles on the Tex in which R〉 1 is the best condition, and there is one-peak structure on the Tex - D plot; （iii） For the case of-1 〈 λ≤ 0, D and its correlation time τ1 play opposite roles on the Tex in which R 〈 1 is the best condition and there is one-peak structure on the Tex - τ2 plot.
文摘Molecular dynamics with the stochastic process provides a convenient way to compute structural and thermodynamic properties of chemical, biological, and materials systems. It is demonstrated that the virtual dynamics case that we proposed for the Langevin equation [J. Chem. Phys. 147, 184104 （2017）] in principle exists in other types of stochastic thermostats as well. The recommended ＂middle＂ scheme [J. Chem. Phys. 147, 034109 （2017）] of the Andersen thermostat is investigated as an example. As shown by both analytic and numerical results, while the real and virtual dynamics cases approach the same plateau of the characteristic correlation time in the high collision frequency limit, the accuracy and efficiency of sampling are relatively insensitive to the value of the collision frequency in a broad range. After we compare the behaviors of the Andersen thermostat to those of Langevin dynamics, a heuristic schematic representation thermostatting processes with molecular is proposed for understanding efficient stochastic dynamics.
文摘Supported by a new generation of mobile devices, e-commerce is now in the process of being converted into m-commerce. While the traditional fixed PC access to the Internet continues to be important, the mobile access appears to attract more people because of its flexibility. The purpose of this paper is to develop and analyze a mathematical model for capturing how e-commerce performance would be affected by the mobile access to the Internet, where the original paper by Sumita and Yoshii （2010） is extended for better reality. The traditional e-commerce via the fixed PC access is compared with m-commerce which accommodates both the fixed PC access and the mobile access. The distribution of the number of products purchased by time t and the distribution of the time required for selling K products are derived explicitly. Numerical examples are given for illustrating behavioral differences between m-commerce consumers and traditional e-commerce consumers.
基金supported by National Natural Science Foundation of China(Grant No.NSFC61402257)National Basic Research Program of China(973 Program)(Grant Nos.2009CB320500+1 种基金2009CB320501)Tsinghua University Self-determined Project(No.2014z21051)
文摘In the design and construction process of Next Generation Internet, it is important to identify the source of each IP packet forwarding accurately, especially for the support of precise fine-grained management,control, traceability and improving the trustworthiness of the Internet. This paper designed a scalable Network Identity(NID) scheme for the Internet users, proposed NIDTGA(Network Identity and Time Generated Address), an IPv6 address generation algorithm embedded NID and time information, then designed and implemented an IPv6 address generation and traceback system based on NIDTGA. The design of NIDTGA, which reflects the length, time and owner attributes of the IP address, can be a good support to ADN(Address Driven Network). At the same time, by embedding the key elements of user identity and time in the IPv6 address,and by taking into account both the traceability and privacy, NIDTGA can provide a technical basis for the establishment of the network trust mechanism, and achieve the traceability of security event.
