Taking into consideration the effects of rotation and interior magnetic field during the lifetime of the star, we reconstruct the model of α Cen B to satisfy the latest nonasteroseismic and asteroseismic observationa...Taking into consideration the effects of rotation and interior magnetic field during the lifetime of the star, we reconstruct the model of α Cen B to satisfy the latest nonasteroseismic and asteroseismic observational constraints. We find that the effects can induce a change of about 0.3 μHz in the large frequency spacings and can speed up the star＇s evolution. The model of a Cen B has thereby been improved.展开更多
In order to further optimize welding process of Nb-Ti-Mo microalloyed steel, welding thermal cycles on coarse-grained heat-affected zone （CGHAZ） of welded joints were simulated using Gleeble 1500. The microstructure...In order to further optimize welding process of Nb-Ti-Mo microalloyed steel, welding thermal cycles on coarse-grained heat-affected zone （CGHAZ） of welded joints were simulated using Gleeble 1500. The microstructure and low-temperature impact fracture were investigated using a scanning electron microscope and a pendulum impact machine, respectively. Moreover, the relationship between cooling time ts/5 and the microstructure of CGHAZ was discussed, and the effect of microstructure on impact toughness was also studied. As cooling time increased, martensite fraction decreased from 97.8% （3 s） to 3.0% （60 s）. The fraction of martensite/austenite （M/A） constituent increased from 2.2% （3 s） to 39.0% （60 s）, its shape changed from granular to strip, and the maximum length increased from 2.4 μm （3 s） to 7.0 μm （60 s）. As cooling time increased, the prior austenite grain size increased from 34.0 μm （3 s） to 49.0 gm （60 s）, the impact absorption energy reduced from 101.8 J （5 s） to 7.2 J （60 s）, and the fracture mechanism changed from quasi-cleavage fracture to cleavage fracture. The decreased toughness of CGHAZ was due to the reduction of lath martensite-content, coarsening of original austenite grain, and increase and coarsening of M/A constituent. The heat input was controlled under 7 kJ cm-1 during actual welding for these steels.展开更多
In this study the authors determined the nitrogen isotopes of nitrate and the carbon and nitrogen contents of water samples from the Hongfeng Lake and inflowing streams, and, on this basis, discriminated the extraneou...In this study the authors determined the nitrogen isotopes of nitrate and the carbon and nitrogen contents of water samples from the Hongfeng Lake and inflowing streams, and, on this basis, discriminated the extraneous nitrogen input and the interior nitrogen release (organic matter decomposition) in the lake. The results showed that the amount of extraneous nitrogen input into the Hongfeng Lake increases and the interior nitrogen release from the lake is intensified in winter and spring. Nitrogen mixing is relatively obvious at the catchments between the lake inlet and inflowing streams, while organic matter decomposition (nitrification) is most intense in the middle and lower reaches of the lake. In winter and spring the organic matter decomposition takes place mainly at the middle level of the water column in the middle and lower reaches of the lake, which has a bearing on the abundance of degraded organic matter at this water level. This part of degraded organic matter contains a considerable proportion of hydrogenous nitrogen in the lake.展开更多
We present an exact analytical solution of the gravitational field equations describing a static spherically symmetric anisotropic quark matter distribution. The radial pressure inside the star is assumed to obey a li...We present an exact analytical solution of the gravitational field equations describing a static spherically symmetric anisotropic quark matter distribution. The radial pressure inside the star is assumed to obey a linear equation of state, while the tangential pressure is a complicated function of the radial coordinate. In order to obtain the general solution of the field equations a particular density profile inside the star is also assumed. The anisotropic pressure distribution leads to an increase in the maximum radius and mass of the quark star, which in the present model is around three solar masses.展开更多
The cloud-level zonal winds of Saturn are marked by a substantial equatorially antisymmetric component with a speed of about 50 m s^-1 which, if they are sufficiently deep, can produce measurable odd zonal gravitation...The cloud-level zonal winds of Saturn are marked by a substantial equatorially antisymmetric component with a speed of about 50 m s^-1 which, if they are sufficiently deep, can produce measurable odd zonal gravitational coefficients △J2 k＋1, k = 1, 2, 3, 4. This study, based on solutions of the thermal-gravitational wind equation, provides a theoretical basis for interpreting the odd gravitational coefficients of Saturn in terms of its equatorially antisymmetric zonal flow. We adopt a Saturnian model comprising an ice-rock core, a metallic dynamo region and an outer molecular envelope. We use an equatorially antisymmetric zonal flow that is parameterized, confined in the molecular envelope and satisfies the solvability condition required for the thermal-gravitational wind equation. The structure and amplitude of the zonal flow at the cloud level are chosen to be consistent with observations of Saturn.We calculate the odd zonal gravitational coefficients △J2k＋1, k = 1, 2, 3, 4 by regarding the depth of the equatorially antisymmetric winds as a parameter. It is found that △J3 is-4.197 × 10^-8 if the zonal winds extend about 13 000 km downward from the cloud tops while it is-0.765 × 10^-8 if the depth is about 4000 km. The depth/profile of the equatorially antisymmetric zonal winds can eventually be estimated when the high-precision measurements of the Cassini Grand Finale become available.展开更多
Within the framework of a non-local time-dependent stellar convection theory, we study in detail the effect of turbulent anisotropy on stellar pulsation stability. The results show that anisotropy has no substantial i...Within the framework of a non-local time-dependent stellar convection theory, we study in detail the effect of turbulent anisotropy on stellar pulsation stability. The results show that anisotropy has no substantial influence on pulsation stability of g modes and low-order （radial order nr 〈 5） p modes. The effect of turbulent anisotropy increases as the radial order increases. When turbulent anisotropy is neglected, most high-order （nr 〉 5） p modes of all low-temperature stars become unstable. Fortunately, within a wide range of the anisotropic parameter c3, stellar pulsation stability is not sensitive to the specific value of ca. Therefore it is safe to say that calibration errors of the convective parameter ca do not cause any uncertainty in the calculation of stellar pulsation stability.展开更多
Based on a dynamic model for turbulent convection, we investigate the effects of dissipation and anisotropy of the turbulence on the convective energy transport. We introduce two time scales to describe the dissipati...Based on a dynamic model for turbulent convection, we investigate the effects of dissipation and anisotropy of the turbulence on the convective energy transport. We introduce two time scales to describe the dissipation of the turbulence, and approximate the anisotropy of the turbulence by Rotta's proposal of 'return to isotropy'. The improved turbulence model results in an equation to determine the temperature gradient in the convection zone, which is of similar form as that of the MLT. We apply the improved MLT to solar models, and find that the increases of the anisotropy and decreases of the dissipation of the turbulence reduce the value of the convection parameter a, because these processes enhance the convective energy transfer rate. Compared with the observed solar p-mode frequencies, it is plausible that the dissipation of the turbulence in the solar convection zone should be fairly strong, while the degree of anisotropy of the turbulence plays a less significant role on the structure of the solar convection zone.展开更多
Taking into account the helium and metal diffusion, we explore the possible evolutionary status with a seismic analysis, of the MOST （Microvariability and Oscillations of STars） target： the star e Eri. We adopt dif...Taking into account the helium and metal diffusion, we explore the possible evolutionary status with a seismic analysis, of the MOST （Microvariability and Oscillations of STars） target： the star e Eri. We adopt different input parameters to construct models to fit the available observational constraints in, e.g., Teff, L, R and [Fe/H]. From the computation we obtain the average large spacings of e Eri to be about 194 ± 1μHz. The age of the diffused models was found to be about 1 Gyr, which is younger than the age determined previously by models without diffusion. We found that the effect of pure helium diffusion on the internal structure of the young low-mass star is slight, but that of metal diffusion is obvious. The metal diffusion leads the models to have much higher temperature in the radiative interior, and, correspondingly a higher sound speed there, hence a larger frequency and spacings.展开更多
The aim of this paper is to reduce the losses, total generation cost by switching of transmission line and to maintain voltage security under N - 1 contingency conditions. Generation cost is calculated and the pr...The aim of this paper is to reduce the losses, total generation cost by switching of transmission line and to maintain voltage security under N - 1 contingency conditions. Generation cost is calculated and the priority list is made for switching the line. The problem is solved by ACOPF using Interior Point Method. In order to test the feasibility and effectiveness of the above method, a sample 6-bus system and IEEE 30-bus system have been used. The impact of switching on system parameter includes the generation cost, locational marginal pricing (LMP) and transmission losses, ensuring voltage security of the system.展开更多
基金The Ministry of Science and Technology of the People's Republic of China through Grant 2007CB815406the NSFC through Grants 10173021,10433030,10773003 and 10778601
文摘Taking into consideration the effects of rotation and interior magnetic field during the lifetime of the star, we reconstruct the model of α Cen B to satisfy the latest nonasteroseismic and asteroseismic observational constraints. We find that the effects can induce a change of about 0.3 μHz in the large frequency spacings and can speed up the star＇s evolution. The model of a Cen B has thereby been improved.
基金This work was financially supported by the National Natural Science Foundation of China （No. 51775102）, Open Research Fund from the State Key Laboratory of Roiling and Automation, Northeastern University （No. 2016005） and Project Funded by China Postdoctoral Science Foundation （No. 2016M601877）.
文摘In order to further optimize welding process of Nb-Ti-Mo microalloyed steel, welding thermal cycles on coarse-grained heat-affected zone （CGHAZ） of welded joints were simulated using Gleeble 1500. The microstructure and low-temperature impact fracture were investigated using a scanning electron microscope and a pendulum impact machine, respectively. Moreover, the relationship between cooling time ts/5 and the microstructure of CGHAZ was discussed, and the effect of microstructure on impact toughness was also studied. As cooling time increased, martensite fraction decreased from 97.8% （3 s） to 3.0% （60 s）. The fraction of martensite/austenite （M/A） constituent increased from 2.2% （3 s） to 39.0% （60 s）, its shape changed from granular to strip, and the maximum length increased from 2.4 μm （3 s） to 7.0 μm （60 s）. As cooling time increased, the prior austenite grain size increased from 34.0 μm （3 s） to 49.0 gm （60 s）, the impact absorption energy reduced from 101.8 J （5 s） to 7.2 J （60 s）, and the fracture mechanism changed from quasi-cleavage fracture to cleavage fracture. The decreased toughness of CGHAZ was due to the reduction of lath martensite-content, coarsening of original austenite grain, and increase and coarsening of M/A constituent. The heat input was controlled under 7 kJ cm-1 during actual welding for these steels.
基金The work was supported by the National Natural Science Foundation of China (Grant No. 40173012)the Key and Innovation Project Foundation of the Chinese Academy of Sciences (Grant No. KZCX2-105).
文摘In this study the authors determined the nitrogen isotopes of nitrate and the carbon and nitrogen contents of water samples from the Hongfeng Lake and inflowing streams, and, on this basis, discriminated the extraneous nitrogen input and the interior nitrogen release (organic matter decomposition) in the lake. The results showed that the amount of extraneous nitrogen input into the Hongfeng Lake increases and the interior nitrogen release from the lake is intensified in winter and spring. Nitrogen mixing is relatively obvious at the catchments between the lake inlet and inflowing streams, while organic matter decomposition (nitrification) is most intense in the middle and lower reaches of the lake. In winter and spring the organic matter decomposition takes place mainly at the middle level of the water column in the middle and lower reaches of the lake, which has a bearing on the abundance of degraded organic matter at this water level. This part of degraded organic matter contains a considerable proportion of hydrogenous nitrogen in the lake.
文摘We present an exact analytical solution of the gravitational field equations describing a static spherically symmetric anisotropic quark matter distribution. The radial pressure inside the star is assumed to obey a linear equation of state, while the tangential pressure is a complicated function of the radial coordinate. In order to obtain the general solution of the field equations a particular density profile inside the star is also assumed. The anisotropic pressure distribution leads to an increase in the maximum radius and mass of the quark star, which in the present model is around three solar masses.
基金supported by Leverhulme Trust Research Project(Grant RPG-2015-096)by STFC(Grant ST/R000891/1)+1 种基金by Macao FDCT(Grants007/2016/A1 and 001/2016/AFJ)supported by 1000 Youth Talents Programme of China
文摘The cloud-level zonal winds of Saturn are marked by a substantial equatorially antisymmetric component with a speed of about 50 m s^-1 which, if they are sufficiently deep, can produce measurable odd zonal gravitational coefficients △J2 k＋1, k = 1, 2, 3, 4. This study, based on solutions of the thermal-gravitational wind equation, provides a theoretical basis for interpreting the odd gravitational coefficients of Saturn in terms of its equatorially antisymmetric zonal flow. We adopt a Saturnian model comprising an ice-rock core, a metallic dynamo region and an outer molecular envelope. We use an equatorially antisymmetric zonal flow that is parameterized, confined in the molecular envelope and satisfies the solvability condition required for the thermal-gravitational wind equation. The structure and amplitude of the zonal flow at the cloud level are chosen to be consistent with observations of Saturn.We calculate the odd zonal gravitational coefficients △J2k＋1, k = 1, 2, 3, 4 by regarding the depth of the equatorially antisymmetric winds as a parameter. It is found that △J3 is-4.197 × 10^-8 if the zonal winds extend about 13 000 km downward from the cloud tops while it is-0.765 × 10^-8 if the depth is about 4000 km. The depth/profile of the equatorially antisymmetric zonal winds can eventually be estimated when the high-precision measurements of the Cassini Grand Finale become available.
基金supported by the National Natural Science Foundation of China (NSFC, Grant Nos. 11403039, 11473037 and 11373069)
文摘Within the framework of a non-local time-dependent stellar convection theory, we study in detail the effect of turbulent anisotropy on stellar pulsation stability. The results show that anisotropy has no substantial influence on pulsation stability of g modes and low-order （radial order nr 〈 5） p modes. The effect of turbulent anisotropy increases as the radial order increases. When turbulent anisotropy is neglected, most high-order （nr 〉 5） p modes of all low-temperature stars become unstable. Fortunately, within a wide range of the anisotropic parameter c3, stellar pulsation stability is not sensitive to the specific value of ca. Therefore it is safe to say that calibration errors of the convective parameter ca do not cause any uncertainty in the calculation of stellar pulsation stability.
基金he NSFC under Grants 19625306 and19833040, and National Key Fundamental Research Project "Formation and Evolution of Galaxie
文摘Based on a dynamic model for turbulent convection, we investigate the effects of dissipation and anisotropy of the turbulence on the convective energy transport. We introduce two time scales to describe the dissipation of the turbulence, and approximate the anisotropy of the turbulence by Rotta's proposal of 'return to isotropy'. The improved turbulence model results in an equation to determine the temperature gradient in the convection zone, which is of similar form as that of the MLT. We apply the improved MLT to solar models, and find that the increases of the anisotropy and decreases of the dissipation of the turbulence reduce the value of the convection parameter a, because these processes enhance the convective energy transfer rate. Compared with the observed solar p-mode frequencies, it is plausible that the dissipation of the turbulence in the solar convection zone should be fairly strong, while the degree of anisotropy of the turbulence plays a less significant role on the structure of the solar convection zone.
基金the National Natural Science Foundation of China
文摘Taking into account the helium and metal diffusion, we explore the possible evolutionary status with a seismic analysis, of the MOST （Microvariability and Oscillations of STars） target： the star e Eri. We adopt different input parameters to construct models to fit the available observational constraints in, e.g., Teff, L, R and [Fe/H]. From the computation we obtain the average large spacings of e Eri to be about 194 ± 1μHz. The age of the diffused models was found to be about 1 Gyr, which is younger than the age determined previously by models without diffusion. We found that the effect of pure helium diffusion on the internal structure of the young low-mass star is slight, but that of metal diffusion is obvious. The metal diffusion leads the models to have much higher temperature in the radiative interior, and, correspondingly a higher sound speed there, hence a larger frequency and spacings.
文摘The aim of this paper is to reduce the losses, total generation cost by switching of transmission line and to maintain voltage security under N - 1 contingency conditions. Generation cost is calculated and the priority list is made for switching the line. The problem is solved by ACOPF using Interior Point Method. In order to test the feasibility and effectiveness of the above method, a sample 6-bus system and IEEE 30-bus system have been used. The impact of switching on system parameter includes the generation cost, locational marginal pricing (LMP) and transmission losses, ensuring voltage security of the system.
