Laser forraing is a new flexible and dieless forming technique. To achieve the high accuracy forming, the temperature gradient mechanism （TGM） is studied. In the analysis of TGM, the plate bends about x-axis and abo...Laser forraing is a new flexible and dieless forming technique. To achieve the high accuracy forming, the temperature gradient mechanism （TGM） is studied. In the analysis of TGM, the plate bends about x-axis and about y-axis as well. To understand the deformation trend, the numerical simulation of deformation of plate is conducted by choosing different laser powers, laser spot diameters, scanning speeds, lengths, widths and thicknesses. From the results of simulation, it can be seen that the laser spot diameter, the scanning speed, laser power and thickness of plate play dominant roles in the laser forming process. However, the bending angles αx and αy show different trends with the variation of parameters. In addition, in comparison with above four parameters, the effect of length and width of plate on the beading angle may be neglected, but their effects are significant for the bending radius R.展开更多
Plant life form diversity and its direct gradient analysis on a larger scale climate change gradient were tested, based on the data from Northeast China Transect platform. The results showed that the species numbers, ...Plant life form diversity and its direct gradient analysis on a larger scale climate change gradient were tested, based on the data from Northeast China Transect platform. The results showed that the species numbers, life form richness and life form diversity were relative higher at the eastern forests and the ecotone between typical vegetation, while those on the meadow grasslands and typical steppes were lower. Although plant life forms can reflect the climate variations, life form diversity is not consistent with the major global gradient along the NECT.展开更多
The combined application of organic fertilizer and chemical fertilizer is an effective measure to increase nutrient content of soil plough layer, which must have a profound impact on the deep soil nutrients, especiall...The combined application of organic fertilizer and chemical fertilizer is an effective measure to increase nutrient content of soil plough layer, which must have a profound impact on the deep soil nutrients, especially the contents of nitrogen forms. The purpose of this study was to explore the characteristics of soil nitrogen forms in plough layer and along depth gradient in different fertilization treatments, so as to evaluate the soil quality in spatial dimension, further provid</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> a theoretical basis for scientific fertilization and improvement of paddy soil fertility. Here, a 34-year field experiment was conducted with three treatments: without any fertilizer (CK), pure chemical fertilizer (NPK) and chemical fertilizer combined with organic fertilizer (NPKM). We analyzed the content of nitrogen forms in 0 - 100 cm soil depth and their ratios to total nitrogen (TN), and discussed the correlation between nitrogen forms contents and pH, CEC. Results showed that, compared with CK, both NPK and NPKM significantly increased the contents of nitrogen forms in topsoil (soil layer of 0 - 20 cm), especially nitrate nitrogen (NO<sub>3</sub><sup style="margin-left:-6px;">-</sup>-N) content increased by 70% (NPK) and 111% (NPKM), respectively. Although the contents of different nitrogen forms decreased gradually along soil depth gradient, NPKS slowed down the decline rate of TN and alkali-hydrolysable nitrogen (AN) in 0 - 60 cm soil layer, compared to CK. Compared to NPK, NPKM significantly increased the NO<sub>3</sub><sup style="margin-left:-6px;">-</sup>-N/TN ratio in 0 - 20 cm soil layer, but also decreased the content of </span><span><span></span><span style="font-family:Verdana;">-N in 20 - 40 cm, which was beneficial to reduce the risk of nitrogen leaching caused by nitrate leaching into deep layer. The increase of soil pH in NPKM treatment obviously alleviated the problem of soil acidification caused by long-term application of chemical fertilizer. Correlation analysis showed that there was a significant positive correlation between soil nitrogen forms and cation exchange capacity (CEC), but no significant correlation with soil pH. In conclusion, NPKM ensured the nutrients of soil plough layer (0 - 20 cm), also reduced the risk of nitrogen infiltration and nitrogen loss, thus ensur</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> the fertility of soil profile.展开更多
The idea about preparation of Re-Mo-Ti alloy is put forward because of applications of Re and Mo-Re alloys in aerospace.Basing on the thermodynamics theory,the feasibility of developing a new high temperature alloy Re...The idea about preparation of Re-Mo-Ti alloy is put forward because of applications of Re and Mo-Re alloys in aerospace.Basing on the thermodynamics theory,the feasibility of developing a new high temperature alloy Re-Mo-Ti is investigated.The solid solution forming enthalpies of binary alloys Re-Ti,Mo-Ti and Mo-Re are calculated with the Miedema thermodynamics theory.The Miedema theory of binary alloy can be used in ternary alloy through Kohler model or Toop model.The calculated results show that the forming enthalpies of binary alloys Re-Ti,Ti-Mo and Re-Mo are negative,which indicates that binary alloys Re-Ti,Ti-Mo and Re-Mo can form solid solution in wider component area.The forming enthalpies of Re-Mo-Ti ternary alloy are still negative and smaller than those of binary alloys Re-Ti,Ti-Mo or Re-Mo,which indicates it is possible to form large solid solution graph area among ternary alloys of Ti,Mo,Re elements.It is feasible to develop a new high temperature material in thermodynamics,in this material Re-Mo-Ti solid solution as base phase,and the Ti5Re24 intermetallic compounds or interphase ω (Ti4Mo3) as strengthening phase.展开更多
The wear behavior of Ni-based single crystal(NBSC)superalloy SRR99 fabricated by laser-directed energy deposition(LDED)is investigated and compared with that of its cast counterpart.While γ'precipitate size in th...The wear behavior of Ni-based single crystal(NBSC)superalloy SRR99 fabricated by laser-directed energy deposition(LDED)is investigated and compared with that of its cast counterpart.While γ'precipitate size in the latter is>400 nm,that in the former is an order of magnitude lower.Dry sliding wear tests reveal that the wear rate and coefficient of friction of the LDED alloy are 75% and 20%lower than that of its cast counterpart,respectively.Detailed transmission electron microscopy investigation of the wear-tested cast alloy indicates that there is orientation change and formation of nanoscale grains only at the top layer of the worn surface,whereas regions below undergo moderate plastic deformation via dislocation slip.In contrast,the sub-surface of the worn LDED alloy has a graded microstructure,with a composite of NiO/γ-Ni on the top,γ'free nano-grains in the middle,and a highly deformed nanoscale layer at the bottom.The improved wear behavior of the LDED alloy is attributed to its higher dislocation density,finerγ'precipitates,and the formation of this graded microstructure.Finally,a detailed description of mechanisms that lead to the formation of this unique graded microstructure is provided.展开更多
The current study performed a finite element analysis of the strain localization behavior of a voided ductile material using a non-local plasticity formulation in which the yield strength depends on both an equivalent...The current study performed a finite element analysis of the strain localization behavior of a voided ductile material using a non-local plasticity formulation in which the yield strength depends on both an equivalent plastic strain measurement (hardening parameter) and Laplacian equivalent. The introduction of gradient terms to the yield function was found to play an important role in simulating the strain localization behavior of the voided ductile material. The effect of the mesh size and characteristic length on the strain localization were also investigated. An FEM simulation based on the proposed non-local plasticity revealed that the load-strain curves of the voided ductile material subjected to plane strain tension converged to one curve, regardless of the mesh size. In addition, the results using non-local plasticity also exhibited that the dependence of the deformation behavior of the material on the mesh size was much less sensitive than that with classical local plasticity and could be successfully eliminated through the introduction of a large value for the characteristic length.展开更多
针对智能反射面(IRS, intelligent reflecting surface)辅助的多输入单输出(MISO, multiple input singleoutput)无线携能通信(SWIPT, simultaneous wireless information and power transfer)系统,考虑基站最大发射功率、IRS反射相移...针对智能反射面(IRS, intelligent reflecting surface)辅助的多输入单输出(MISO, multiple input singleoutput)无线携能通信(SWIPT, simultaneous wireless information and power transfer)系统,考虑基站最大发射功率、IRS反射相移矩阵的单位膜约束和能量接收器的最小能量约束,以最大化信息传输速率为目标,联合优化了基站处的波束成形向量和智能反射面的反射波束成形向量。为解决非凸优化问题,提出了一种基于深度强化学习的深度确定性策略梯度(DDPG, deep deterministic policy gradient)算法。仿真结果表明,DDPG算法的平均奖励与学习率有关,在选取合适的学习率的条件下,DDPG算法能获得与传统优化算法相近的平均互信息,但运行时间明显低于传统的非凸优化算法,即使增加天线数和反射单元数,DDPG算法依然可以在较短的时间内收敛。这说明DDPG算法能有效地提高计算效率,更适合实时性要求较高的通信业务。展开更多
文摘Laser forraing is a new flexible and dieless forming technique. To achieve the high accuracy forming, the temperature gradient mechanism （TGM） is studied. In the analysis of TGM, the plate bends about x-axis and about y-axis as well. To understand the deformation trend, the numerical simulation of deformation of plate is conducted by choosing different laser powers, laser spot diameters, scanning speeds, lengths, widths and thicknesses. From the results of simulation, it can be seen that the laser spot diameter, the scanning speed, laser power and thickness of plate play dominant roles in the laser forming process. However, the bending angles αx and αy show different trends with the variation of parameters. In addition, in comparison with above four parameters, the effect of length and width of plate on the beading angle may be neglected, but their effects are significant for the bending radius R.
文摘Plant life form diversity and its direct gradient analysis on a larger scale climate change gradient were tested, based on the data from Northeast China Transect platform. The results showed that the species numbers, life form richness and life form diversity were relative higher at the eastern forests and the ecotone between typical vegetation, while those on the meadow grasslands and typical steppes were lower. Although plant life forms can reflect the climate variations, life form diversity is not consistent with the major global gradient along the NECT.
文摘The combined application of organic fertilizer and chemical fertilizer is an effective measure to increase nutrient content of soil plough layer, which must have a profound impact on the deep soil nutrients, especially the contents of nitrogen forms. The purpose of this study was to explore the characteristics of soil nitrogen forms in plough layer and along depth gradient in different fertilization treatments, so as to evaluate the soil quality in spatial dimension, further provid</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> a theoretical basis for scientific fertilization and improvement of paddy soil fertility. Here, a 34-year field experiment was conducted with three treatments: without any fertilizer (CK), pure chemical fertilizer (NPK) and chemical fertilizer combined with organic fertilizer (NPKM). We analyzed the content of nitrogen forms in 0 - 100 cm soil depth and their ratios to total nitrogen (TN), and discussed the correlation between nitrogen forms contents and pH, CEC. Results showed that, compared with CK, both NPK and NPKM significantly increased the contents of nitrogen forms in topsoil (soil layer of 0 - 20 cm), especially nitrate nitrogen (NO<sub>3</sub><sup style="margin-left:-6px;">-</sup>-N) content increased by 70% (NPK) and 111% (NPKM), respectively. Although the contents of different nitrogen forms decreased gradually along soil depth gradient, NPKS slowed down the decline rate of TN and alkali-hydrolysable nitrogen (AN) in 0 - 60 cm soil layer, compared to CK. Compared to NPK, NPKM significantly increased the NO<sub>3</sub><sup style="margin-left:-6px;">-</sup>-N/TN ratio in 0 - 20 cm soil layer, but also decreased the content of </span><span><span></span><span style="font-family:Verdana;">-N in 20 - 40 cm, which was beneficial to reduce the risk of nitrogen leaching caused by nitrate leaching into deep layer. The increase of soil pH in NPKM treatment obviously alleviated the problem of soil acidification caused by long-term application of chemical fertilizer. Correlation analysis showed that there was a significant positive correlation between soil nitrogen forms and cation exchange capacity (CEC), but no significant correlation with soil pH. In conclusion, NPKM ensured the nutrients of soil plough layer (0 - 20 cm), also reduced the risk of nitrogen infiltration and nitrogen loss, thus ensur</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> the fertility of soil profile.
基金the Shanghai Leading Academic Discipline Project of China (No.J51402)the Innovation Program of Shanghai Municipal Education Commission of China (No.11ZZ177)
文摘The idea about preparation of Re-Mo-Ti alloy is put forward because of applications of Re and Mo-Re alloys in aerospace.Basing on the thermodynamics theory,the feasibility of developing a new high temperature alloy Re-Mo-Ti is investigated.The solid solution forming enthalpies of binary alloys Re-Ti,Mo-Ti and Mo-Re are calculated with the Miedema thermodynamics theory.The Miedema theory of binary alloy can be used in ternary alloy through Kohler model or Toop model.The calculated results show that the forming enthalpies of binary alloys Re-Ti,Ti-Mo and Re-Mo are negative,which indicates that binary alloys Re-Ti,Ti-Mo and Re-Mo can form solid solution in wider component area.The forming enthalpies of Re-Mo-Ti ternary alloy are still negative and smaller than those of binary alloys Re-Ti,Ti-Mo or Re-Mo,which indicates it is possible to form large solid solution graph area among ternary alloys of Ti,Mo,Re elements.It is feasible to develop a new high temperature material in thermodynamics,in this material Re-Mo-Ti solid solution as base phase,and the Ti5Re24 intermetallic compounds or interphase ω (Ti4Mo3) as strengthening phase.
基金supported by the National Key R&D Program of China(Grant Nos.2023YFB3712002 and 2021YFB3702503)the National Natural Science Foundation of China(Grant Nos.51927801 and U2032205)the National Science and Technology Major Project(Grant Nos.Y2019-VII-0011-0151 and 2019-VII-0019-0161)。
文摘The wear behavior of Ni-based single crystal(NBSC)superalloy SRR99 fabricated by laser-directed energy deposition(LDED)is investigated and compared with that of its cast counterpart.While γ'precipitate size in the latter is>400 nm,that in the former is an order of magnitude lower.Dry sliding wear tests reveal that the wear rate and coefficient of friction of the LDED alloy are 75% and 20%lower than that of its cast counterpart,respectively.Detailed transmission electron microscopy investigation of the wear-tested cast alloy indicates that there is orientation change and formation of nanoscale grains only at the top layer of the worn surface,whereas regions below undergo moderate plastic deformation via dislocation slip.In contrast,the sub-surface of the worn LDED alloy has a graded microstructure,with a composite of NiO/γ-Ni on the top,γ'free nano-grains in the middle,and a highly deformed nanoscale layer at the bottom.The improved wear behavior of the LDED alloy is attributed to its higher dislocation density,finerγ'precipitates,and the formation of this graded microstructure.Finally,a detailed description of mechanisms that lead to the formation of this unique graded microstructure is provided.
文摘The current study performed a finite element analysis of the strain localization behavior of a voided ductile material using a non-local plasticity formulation in which the yield strength depends on both an equivalent plastic strain measurement (hardening parameter) and Laplacian equivalent. The introduction of gradient terms to the yield function was found to play an important role in simulating the strain localization behavior of the voided ductile material. The effect of the mesh size and characteristic length on the strain localization were also investigated. An FEM simulation based on the proposed non-local plasticity revealed that the load-strain curves of the voided ductile material subjected to plane strain tension converged to one curve, regardless of the mesh size. In addition, the results using non-local plasticity also exhibited that the dependence of the deformation behavior of the material on the mesh size was much less sensitive than that with classical local plasticity and could be successfully eliminated through the introduction of a large value for the characteristic length.
文摘针对智能反射面(IRS, intelligent reflecting surface)辅助的多输入单输出(MISO, multiple input singleoutput)无线携能通信(SWIPT, simultaneous wireless information and power transfer)系统,考虑基站最大发射功率、IRS反射相移矩阵的单位膜约束和能量接收器的最小能量约束,以最大化信息传输速率为目标,联合优化了基站处的波束成形向量和智能反射面的反射波束成形向量。为解决非凸优化问题,提出了一种基于深度强化学习的深度确定性策略梯度(DDPG, deep deterministic policy gradient)算法。仿真结果表明,DDPG算法的平均奖励与学习率有关,在选取合适的学习率的条件下,DDPG算法能获得与传统优化算法相近的平均互信息,但运行时间明显低于传统的非凸优化算法,即使增加天线数和反射单元数,DDPG算法依然可以在较短的时间内收敛。这说明DDPG算法能有效地提高计算效率,更适合实时性要求较高的通信业务。
