摘要 :
As the future highest dam in the world，Shuang Jiang Kou rockfill dam was the water retaining structure of homonymous hydropower station，a controlling engineering on Da Du River hydropower development，which is under design ...
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As the future highest dam in the world，Shuang Jiang Kou rockfill dam was the water retaining structure of homonymous hydropower station，a controlling engineering on Da Du River hydropower development，which is under design now.This dam is a central earth core dam with a height of 312 meters.A type of gravel soil stiffer than clay，which is made by artificial compounding of clay and gravel，is introduced to reduce the difference in displacement of earth core and rock filled shell zone.A three dimensional coupled nonlinear finite element analysis is carried out to study the three dimensional stressstrain behavior of Shuang Jiang Kou rockfill dam. Computation results show that the introduction of the contact high-plasticity clay layer is effective and necessary.
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摘要 :
As the future highest dam in the world，Shuang Jiang Kou rockfill dam was the water retaining structure of homonymous hydropower station，a controlling engineering on Da Du River hydropower development，which is under design now.T...
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As the future highest dam in the world，Shuang Jiang Kou rockfill dam was the water retaining structure of homonymous hydropower station，a controlling engineering on Da Du River hydropower development，which is under design now.This dam is a central earth core dam with a height of 312 meters.A type of gravel soil stiffer than clay，which is made by artificial compounding of clay and gravel，is introduced to reduce the difference in displacement of earth core and rock filled shell zone.A three dimensional coupled nonlinear finite element analysis is carried out to study the three dimensional stressstrain behavior of Shuang Jiang Kou rockfill dam. Computation results show that the introduction of the contact high-plasticity clay layer is effective and necessary.
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摘要 :
For traditional linear Stirling Cryocoolers, the amplitude of output sinusoidal AC voltage is modulated mainly by Modulation ratio (M) controlled by the inverter, so that the compression piston is driven to perform linear reciproc...
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For traditional linear Stirling Cryocoolers, the amplitude of output sinusoidal AC voltage is modulated mainly by Modulation ratio (M) controlled by the inverter, so that the compression piston is driven to perform linear reciprocating motion and the compressed refrigerant expands rapidly in the expander to achieve the purpose of refrigeration. In practice, however, when M is used to modulate the amplitude of sinusoidal AC voltage, the input power and current will increase to a certain extent with the decreased M. To address the aforementioned concern, the correlated characteristics of output voltage of the inverter under the M and vector phase shift modes will be compared and analyzed in this paper for the selection of best driving mode for linear Stirling cryocoolers. Although the experiments reveal a small difference of sinusoidal voltage amplitude of the two modes under the same input voltage, and a basically same energy distribution of waveform at the fundamental frequency and other frequency multiplications, the required power and current are more stable and do not increase with the decreased output voltage amplitude in the mode of vector phase shift.
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In Voltage Source Converter-based High Voltage DC transmission (VSC-HVDC), the unbalance of AC grid is caused by the power quality deterioration, such as AC grid current disturbance and DC voltage periodic ripple. Firstly, the for...
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In Voltage Source Converter-based High Voltage DC transmission (VSC-HVDC), the unbalance of AC grid is caused by the power quality deterioration, such as AC grid current disturbance and DC voltage periodic ripple. Firstly, the forming reason of system power ripple is introduced under the unbalance of AC grid. An optimal control strategy for AC and DC is proposed. Taking the instantaneous active power without ripple, the voltage outer-loop based on sliding mode control is designed. Secondly, a grid current control under single d-q frame is proposed. With the VSC mathematical model of single d-q frame under the unbalance AC grid conditions, and the reference expressions of positive and negative sequence current components under single positive sequence d-q frame are obtained according the reverse-model principle. Furthermore, the proportional integral plus repetitive control strategy is proposed to implement the control of the current under the single d-q frame, as a result, the effect of the AC grid unbalance on the AC and DC power quality of VSC can be reduced. The corresponding simulation results verify the accuracy and feasibility of the proposed strategy.
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摘要 :
In Voltage Source Converter-based High Voltage DC transmission (VSC-HVDC), the unbalance of AC grid is caused by the power quality deterioration, such as AC grid current disturbance and DC voltage periodic ripple. Firstly, the for...
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In Voltage Source Converter-based High Voltage DC transmission (VSC-HVDC), the unbalance of AC grid is caused by the power quality deterioration, such as AC grid current disturbance and DC voltage periodic ripple. Firstly, the forming reason of system power ripple is introduced under the unbalance of AC grid. An optimal control strategy for AC and DC is proposed. Taking the instantaneous active power without ripple, the voltage outer-loop based on sliding mode control is designed. Secondly, a grid current control under single d-q frame is proposed. With the VSC mathematical model of single d-q frame under the unbalance AC grid conditions, and the reference expressions of positive and negative sequence current components under single positive sequence d-q frame are obtained according the reverse-model principle. Furthermore, the proportional integral plus repetitive control strategy is proposed to implement the control of the current under the single d-q frame, as a result, the effect of the AC grid unbalance on the AC and DC power quality of VSC can be reduced. The corresponding simulation results verify the accuracy and feasibility of the proposed strategy.
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摘要 :
In Voltage Source Converter-based High Voltage DC transmission (VSC-HVDC), the unbalance of AC grid is caused by the power quality deterioration, such as AC grid current disturbance and DC voltage periodic ripple. Firstly, the for...
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In Voltage Source Converter-based High Voltage DC transmission (VSC-HVDC), the unbalance of AC grid is caused by the power quality deterioration, such as AC grid current disturbance and DC voltage periodic ripple. Firstly, the forming reason of system power ripple is introduced under the unbalance of AC grid. An optimal control strategy for AC and DC is proposed. Taking the instantaneous active power without ripple, the voltage outer-loop based on sliding mode control is designed. Secondly, a grid current control under single d-q frame is proposed. With the VSC mathematical model of single d-q frame under the unbalance AC grid conditions, and the reference expressions of positive and negative sequence current components under single positive sequence d-q frame are obtained according the reverse-model principle. Furthermore, the proportional integral plus repetitive control strategy is proposed to implement the control of the current under the single d-q frame, as a result, the effect of the AC grid unbalance on the AC and DC power quality of VSC can be reduced. The corresponding simulation results verify the accuracy and feasibility of the proposed strategy.
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摘要 :
The range of trend of oil price will be decided by marginal production cost of crude oil and production cost of alternative energy consumed as transportation fuel on a large scale. The former factor determines the lower limit and ...
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The range of trend of oil price will be decided by marginal production cost of crude oil and production cost of alternative energy consumed as transportation fuel on a large scale. The former factor determines the lower limit and the latter determines the upper limit of oil price. With increasing difficulty of oil production increment, the marginal cost will increase gradually and the lower limit of oil price will go up; however, with the advancement of technology, the production cost of alternative energy will be lowered. With combination of aforementioned two factors, the range of oil price trend will be narrowed. As the oil market is commercialized, financial factors and the value of USD will not only affect the short-term change of oil price, they may become fundamentals factors that exert influence on the mid-long term change of oil price, namely, "New Fundamentals", which will determine the fluctuation degree of oil price in the long run.
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摘要 :
The range of trend of oil price will be decided by marginal production cost of crude oil and production cost of alternative energy consumed as transportation fuel on a large scale. The former factor determines the lower limit and ...
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The range of trend of oil price will be decided by marginal production cost of crude oil and production cost of alternative energy consumed as transportation fuel on a large scale. The former factor determines the lower limit and the latter determines the upper limit of oil price. With increasing difficulty of oil production increment, the marginal cost will increase gradually and the lower limit of oil price will go up; however, with the advancement of technology, the production cost of alternative energy will be lowered. With combination of aforementioned two factors, the range of oil price trend will be narrowed. As the oil market is commercialized, financial factors and the value of USD will not only affect the short-term change of oil price, they may become fundamentals factors that exert influence on the mid-long term change of oil price, namely, "New Fundamentals", which will determine the fluctuation degree of oil price in the long run.
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The genetically engineered bacteria,expressing the fusion protein of enhanced green fluorescent protein(EGFP)and carboxylesterase Bl, have been successfully constructed, by cloning thegenes of EGFP and carboxylesterase Bl into the...
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The genetically engineered bacteria,expressing the fusion protein of enhanced green fluorescent protein(EGFP)and carboxylesterase Bl, have been successfully constructed, by cloning thegenes of EGFP and carboxylesterase Bl into the pET-28b vector and then transforming E. coli BL21(DE3). Expression of the fusion protein can be induced in E. coli BL21(DE3)at 28 deg C for 8 h by even as little as 0. 01 mM isopropyl beta-D-thiogalactopyranoside(IPTG). The genetically engineeredbacteria not only can degrade pesticides in the environment but also can be found easily by fluorescence spectrophotometry. The green fluorescence emitted by EGFP in genetically engineered bacteria can be seen even by naked eye in daylight.
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On one hand, major shareholders can use the excessive control right to expropriate interests from other small shareholders and managers, transfer assets of listed companies to meet their own interests and reduce the value of compa...
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On one hand, major shareholders can use the excessive control right to expropriate interests from other small shareholders and managers, transfer assets of listed companies to meet their own interests and reduce the value of companies, which is expressed as "entrenchment effect"; On the other hand, the legal environment in China is imperfect and lacks effective monitor system to protect the interests of shareholders. Major shareholders can use their control to monitor managers effectively, so it will reduce the agency costs and increase the value of companies, which is "alignment effect". In this paper, we use no-parameter model and fixed effect model to estimate the relationship between the above effects and the percentage of the largest shareholders, and find that with the increase of the largest shareholders' shares, the performance of Chinese listed companies shows an N-type curve, representing "alignment effect"-"entrenchment effect"-"alignment effect" by turns. The attributes of the largest shareholders are also connected with the two effects, and the state-owned shareholders are easier to display the behaviors of "the entrenchment effect", inducing that the performance is lower than the individual shares, and legal institute shares and foreign shares are not significantly connected with the performance; the introduction of other shareholders can effectively limit the largest shareholders and improve the performance of companies.
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