The three-dimensional teaching mode is an integrated teaching mode,which integrates teaching design,teaching methods,teaching resources and student learning.In the English classroom,the three-dimensional teaching mode...The three-dimensional teaching mode is an integrated teaching mode,which integrates teaching design,teaching methods,teaching resources and student learning.In the English classroom,the three-dimensional teaching mode is used to make the English learning class full of vitality and to improve the effect of English classroom teaching.展开更多
[Objective] The research aimed to study the establishment of a kind of three-dimensional thunderstorm cloud electrification-discharge mode.[Method] Based on a kind of three-dimensional strong convective cloud mode,sev...[Objective] The research aimed to study the establishment of a kind of three-dimensional thunderstorm cloud electrification-discharge mode.[Method] Based on a kind of three-dimensional strong convective cloud mode,several parameterization schemes of electrification-discharge mechanism which were mature and had experimental basis were coupled into the strong convective cloud mode.The three-dimensional strong convective mode could simulate electrification-discharge process,and the three-dimensional thunderstorm cloud electrification-discharge mode was established.[Result] By numerical simulation method,a kind of three-dimensional thunderstorm cloud electrification-discharge mode was established.The mode not only could assess the relative importance of various kinds of electrification mechanisms under different environments,but also described formation of charge center and electrical field within the thunderstorm cloud,occurrence position,propagation process and influence on charge distribution of lightning.The most important thing was that it could quantitatively describe the complicated relative relationships between power,microphysics and electric process in the evolution process of thunderstorm cloud.[Conclusion] The research provided powerful foundation for further studying the lightning characteristics of different thunderstorm clouds,the relationships between lightning characteristics and power,microphysical process,and deeply discussing the early-warning forecasting technology of thunderbolt activity.展开更多
We present a stable linear-cavity single longitudinal mode （SLM） erbium-doped silica fiber laser. It consists of four fiber Bragg gratings （FBGs） directly written in a section of photosensitive erbium-doped fiber ...We present a stable linear-cavity single longitudinal mode （SLM） erbium-doped silica fiber laser. It consists of four fiber Bragg gratings （FBGs） directly written in a section of photosensitive erbium-doped fiber （EDF） to form an asymmetric three-cavity structure. The stable SLM operation at a wavelength of 1545.112 nm with a 3-dB bandwidth of 0.012 nm and an optical signal-to-noise ratio （OSNR） of about 60 dB is verified experimentally. Under laboratory conditions, the performance of a power fluctuation of less than 0.05 dB observed from the power meter for 6 h and a wavelength variation of less than 0.01 nm obtained from the optical spectrum analyzer （OSA） for about 1.5 h are demonstrated. The gain fiber length is no longer limited to only several centimeters for SLM operation because of the excellent mode-selecting ability of the asymmetric three-cavity structure. The proposed scheme provides a simple and cost-effective approach to realizing a stable SLM fiber laser.展开更多
In this work,trapped mode frequencies are computed for a submerged horizontal circular cylinder with the hydrodynamic set-up involving an infinite depth three-layer incompressible fluid with layer-wise different densi...In this work,trapped mode frequencies are computed for a submerged horizontal circular cylinder with the hydrodynamic set-up involving an infinite depth three-layer incompressible fluid with layer-wise different densities.The impermeable cylinder is fully immersed in either the bottom layer or the upper layer.The effect of surface tension at the surface of separation is neglected.In this set-up,there exist three wave numbers:the lowest one on the free surface and the other two on the internal interfaces.For each wave number,there exist two modes for which trapped waves exist.The existence of these trapped modes is shown by numerical evidence.We investigate the variation of these trapped modes subject to change in the depth of the middle layer as well as the submergence depth.We show numerically that two-layer and single-layer results cannot be recovered in the double and single limiting cases of the density ratios tending to unity.The existence of trapped modes shows that in general,a radiation condition for the waves at infinity is insufficient for the uniqueness of the solution of the scattering problem.展开更多
To investigate the methodology and evaluate the clinical value of surface mode on three- dimensional ultrasonography (3DUS) in static anatomical structures, 62 patients with various diseases were studied. The equipmen...To investigate the methodology and evaluate the clinical value of surface mode on three- dimensional ultrasonography (3DUS) in static anatomical structures, 62 patients with various diseases were studied. The equipment used here was Voluson 530D 3DUS imaging system and 3D volume trahsducer with frequency being 3. 0-5. 0 MHz. The 3DUS rendering method was surface mode. The results showed that: 1 ) Surface mode of 3DUS could demonstrate clearly the anatomical characteristics of the region-of-interest (ROI) and the inner wall of lesions or organs that contained fluid. The anatomic details, such as location, size, shape, and number of the ROI, could be visualized intuitively; 2) The outer anatomic features (e. g. contour, edge, configuration, etc. ) of some organs or lesions surrounded by fluid could be displayed clearly. It could be concluded that surface mode on 3DUS could provide more diagnostic information than two-dimensional ultrasonography (2DUS) in some cases and could served as a beneficial supplement to ZDUS in clinical practice.展开更多
The Three Gorges Project (TGP) is the largest concrete structure in the world to this day. The project, with a total amount of approximately 28 million m 3 of concrete, is characterized by complicated structures, inte...The Three Gorges Project (TGP) is the largest concrete structure in the world to this day. The project, with a total amount of approximately 28 million m 3 of concrete, is characterized by complicated structures, intensive construction and high technical standards, which should not only meet the requirements of stability but of special flood releasing, power generation and navigation improvement. Through a decade of engineering practice, a management mode that embodies the characteristics of TGP under construction has been formed. Various new techniques and technologies have been used to ensure the concrete quality. Design, construction and management measures adopted for the concrete works of the project are discussed in this article on an overall basis.展开更多
In this paper, a voltage oriented control strategy for three-level PWM rectifier based on Sliding Mode Control (SMC) is introduced in order to obtain fast and accurate response of dc-bus voltage. To verify the validit...In this paper, a voltage oriented control strategy for three-level PWM rectifier based on Sliding Mode Control (SMC) is introduced in order to obtain fast and accurate response of dc-bus voltage. To verify the validity of the analysis and the feasibility of the proposed control method a set of simulation tests have been conducted using Matlab/Simulink. The simulation results show that compared to the conventional PI controller, the SMC can reduce drastically the three-level rectifier’s voltage fluctuation and improve the dynamic response of dc-bus significantly.展开更多
文摘The three-dimensional teaching mode is an integrated teaching mode,which integrates teaching design,teaching methods,teaching resources and student learning.In the English classroom,the three-dimensional teaching mode is used to make the English learning class full of vitality and to improve the effect of English classroom teaching.
文摘[Objective] The research aimed to study the establishment of a kind of three-dimensional thunderstorm cloud electrification-discharge mode.[Method] Based on a kind of three-dimensional strong convective cloud mode,several parameterization schemes of electrification-discharge mechanism which were mature and had experimental basis were coupled into the strong convective cloud mode.The three-dimensional strong convective mode could simulate electrification-discharge process,and the three-dimensional thunderstorm cloud electrification-discharge mode was established.[Result] By numerical simulation method,a kind of three-dimensional thunderstorm cloud electrification-discharge mode was established.The mode not only could assess the relative importance of various kinds of electrification mechanisms under different environments,but also described formation of charge center and electrical field within the thunderstorm cloud,occurrence position,propagation process and influence on charge distribution of lightning.The most important thing was that it could quantitatively describe the complicated relative relationships between power,microphysics and electric process in the evolution process of thunderstorm cloud.[Conclusion] The research provided powerful foundation for further studying the lightning characteristics of different thunderstorm clouds,the relationships between lightning characteristics and power,microphysical process,and deeply discussing the early-warning forecasting technology of thunderbolt activity.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61077069 and 61107094)the Innovation Foundation for Excellent Doctoral Candidates of Beijing Jiaotong University, China (Grant No. 2011YJS202)
文摘We present a stable linear-cavity single longitudinal mode （SLM） erbium-doped silica fiber laser. It consists of four fiber Bragg gratings （FBGs） directly written in a section of photosensitive erbium-doped fiber （EDF） to form an asymmetric three-cavity structure. The stable SLM operation at a wavelength of 1545.112 nm with a 3-dB bandwidth of 0.012 nm and an optical signal-to-noise ratio （OSNR） of about 60 dB is verified experimentally. Under laboratory conditions, the performance of a power fluctuation of less than 0.05 dB observed from the power meter for 6 h and a wavelength variation of less than 0.01 nm obtained from the optical spectrum analyzer （OSA） for about 1.5 h are demonstrated. The gain fiber length is no longer limited to only several centimeters for SLM operation because of the excellent mode-selecting ability of the asymmetric three-cavity structure. The proposed scheme provides a simple and cost-effective approach to realizing a stable SLM fiber laser.
文摘In this work,trapped mode frequencies are computed for a submerged horizontal circular cylinder with the hydrodynamic set-up involving an infinite depth three-layer incompressible fluid with layer-wise different densities.The impermeable cylinder is fully immersed in either the bottom layer or the upper layer.The effect of surface tension at the surface of separation is neglected.In this set-up,there exist three wave numbers:the lowest one on the free surface and the other two on the internal interfaces.For each wave number,there exist two modes for which trapped waves exist.The existence of these trapped modes is shown by numerical evidence.We investigate the variation of these trapped modes subject to change in the depth of the middle layer as well as the submergence depth.We show numerically that two-layer and single-layer results cannot be recovered in the double and single limiting cases of the density ratios tending to unity.The existence of trapped modes shows that in general,a radiation condition for the waves at infinity is insufficient for the uniqueness of the solution of the scattering problem.
文摘To investigate the methodology and evaluate the clinical value of surface mode on three- dimensional ultrasonography (3DUS) in static anatomical structures, 62 patients with various diseases were studied. The equipment used here was Voluson 530D 3DUS imaging system and 3D volume trahsducer with frequency being 3. 0-5. 0 MHz. The 3DUS rendering method was surface mode. The results showed that: 1 ) Surface mode of 3DUS could demonstrate clearly the anatomical characteristics of the region-of-interest (ROI) and the inner wall of lesions or organs that contained fluid. The anatomic details, such as location, size, shape, and number of the ROI, could be visualized intuitively; 2) The outer anatomic features (e. g. contour, edge, configuration, etc. ) of some organs or lesions surrounded by fluid could be displayed clearly. It could be concluded that surface mode on 3DUS could provide more diagnostic information than two-dimensional ultrasonography (2DUS) in some cases and could served as a beneficial supplement to ZDUS in clinical practice.
文摘The Three Gorges Project (TGP) is the largest concrete structure in the world to this day. The project, with a total amount of approximately 28 million m 3 of concrete, is characterized by complicated structures, intensive construction and high technical standards, which should not only meet the requirements of stability but of special flood releasing, power generation and navigation improvement. Through a decade of engineering practice, a management mode that embodies the characteristics of TGP under construction has been formed. Various new techniques and technologies have been used to ensure the concrete quality. Design, construction and management measures adopted for the concrete works of the project are discussed in this article on an overall basis.
文摘In this paper, a voltage oriented control strategy for three-level PWM rectifier based on Sliding Mode Control (SMC) is introduced in order to obtain fast and accurate response of dc-bus voltage. To verify the validity of the analysis and the feasibility of the proposed control method a set of simulation tests have been conducted using Matlab/Simulink. The simulation results show that compared to the conventional PI controller, the SMC can reduce drastically the three-level rectifier’s voltage fluctuation and improve the dynamic response of dc-bus significantly.
