An analytical model of a ring with six yield hinges and two deformable arc segments is presented for. the prediction of the buckle propagation pressure and initiation pressure in offshore pipelines. The configuration ...An analytical model of a ring with six yield hinges and two deformable arc segments is presented for. the prediction of the buckle propagation pressure and initiation pressure in offshore pipelines. The configuration of a fully collapsed ring is considered as a real dumbbell shape with a line touch between two 'bells', instead of the dumbbell shape with a point touch of two diametrically opposite points. Calculations are performed assuming that the dominant effect on the plastic energy dissipation has the circumferential bending mode. For the linear strain-hardening materials it is found that theoretical predictions based on the above model for both propagation pressure and initiation nressure are in good agreement with experimental results of Kyriakides et al.展开更多
The initial condition Ωde(zini)=n^2(1+zini)^-2/4 at zini = 2000,widely used to solve the differential equation of the density of the new agegraphic dark energy(NADE) Ωde,makes the NADE model a single-paramete...The initial condition Ωde(zini)=n^2(1+zini)^-2/4 at zini = 2000,widely used to solve the differential equation of the density of the new agegraphic dark energy(NADE) Ωde,makes the NADE model a single-parameter dark-energy cosmological model.However,we find that this initial condition is only applicable in a flat universe with only dark energy and pressureless matter.In fact,in order to obtain more information from current observational data,such as the cosmic microwave background(CMB) and the baryon acoustic oscillations(BAO),we need to consider the contribution of radiation.For this situation,the initial condition mentioned above becomes invalid.To overcome this shortcoming,we investigate the evolutions of dark energy in matter-dominated and radiation-dominated epochs,and obtain a new initial condition de(zini)=n2(1+zini)-2(1+F(zini))2/4 at z ini = 2000,where F(z)≡Ωr0(1+z)/[Ωm0+Ωr0(1+z)] with Ωr0 and Ωm0 being the current density parameters of radiation and pressureless matter,respectively.This revised initial condition is applicable for the differential equation of Ωde obtained in the standard Friedmann-Robertson-Walker(FRW) universe with dark energy,pressureless matter,radiation,and even spatial curvature,and can still keep the NADE model as a single-parameter model.With the revised initial condition and the observational data of type Ia supernova(SNIa),CMB,and BAO,we finally constrain the NADE model.The results show that the single free parameter n of the NADE model can be constrained tightly.展开更多
On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the Chi... On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……展开更多
Introduction In English teaching, the first task for teachers should be teaching students with clear information about the language they are learning. The presentation stage is the best way to reach this goal. In this...Introduction In English teaching, the first task for teachers should be teaching students with clear information about the language they are learning. The presentation stage is the best way to reach this goal. In this essay, we analyze the importance of this stage. How it is different from the traditional methods -grammatical explanation and translations methods- and its advantages.展开更多
基金Project supported by National Natural Science Foundation
文摘An analytical model of a ring with six yield hinges and two deformable arc segments is presented for. the prediction of the buckle propagation pressure and initiation pressure in offshore pipelines. The configuration of a fully collapsed ring is considered as a real dumbbell shape with a line touch between two 'bells', instead of the dumbbell shape with a point touch of two diametrically opposite points. Calculations are performed assuming that the dominant effect on the plastic energy dissipation has the circumferential bending mode. For the linear strain-hardening materials it is found that theoretical predictions based on the above model for both propagation pressure and initiation nressure are in good agreement with experimental results of Kyriakides et al.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10705041,10975032,11047112,and 11175042)the Program for New Century Excellent Talents at the University of Ministry of Education of China (Grant No. NCET-09-0276)the National Ministry of Education of China(Grant Nos. N100505001 and N110405011)
文摘The initial condition Ωde(zini)=n^2(1+zini)^-2/4 at zini = 2000,widely used to solve the differential equation of the density of the new agegraphic dark energy(NADE) Ωde,makes the NADE model a single-parameter dark-energy cosmological model.However,we find that this initial condition is only applicable in a flat universe with only dark energy and pressureless matter.In fact,in order to obtain more information from current observational data,such as the cosmic microwave background(CMB) and the baryon acoustic oscillations(BAO),we need to consider the contribution of radiation.For this situation,the initial condition mentioned above becomes invalid.To overcome this shortcoming,we investigate the evolutions of dark energy in matter-dominated and radiation-dominated epochs,and obtain a new initial condition de(zini)=n2(1+zini)-2(1+F(zini))2/4 at z ini = 2000,where F(z)≡Ωr0(1+z)/[Ωm0+Ωr0(1+z)] with Ωr0 and Ωm0 being the current density parameters of radiation and pressureless matter,respectively.This revised initial condition is applicable for the differential equation of Ωde obtained in the standard Friedmann-Robertson-Walker(FRW) universe with dark energy,pressureless matter,radiation,and even spatial curvature,and can still keep the NADE model as a single-parameter model.With the revised initial condition and the observational data of type Ia supernova(SNIa),CMB,and BAO,we finally constrain the NADE model.The results show that the single free parameter n of the NADE model can be constrained tightly.
文摘 On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……
文摘Introduction In English teaching, the first task for teachers should be teaching students with clear information about the language they are learning. The presentation stage is the best way to reach this goal. In this essay, we analyze the importance of this stage. How it is different from the traditional methods -grammatical explanation and translations methods- and its advantages.