共查询到20条相似文献，搜索用时 409 毫秒
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顾颖 《华夏少年(简快作文 )》2008,(3)
语言学家亚历山大曾指出:The teacher is just a facilitator.Teachers cannot teach anybody anything.The student is not an empty glass that will be filled with liquid,with knowledge and with wisdom.The teacher can only 相似文献
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王中佳 《中学英语园地(高三版)》2005,(5)
一、表示“伴随”,意为“与……一道”或“跟……一起”。例如:A wom an with two children is walking down the road.一位妇女和两个孩子正沿着这条路向下走。The teachercam e into the classroom with a sm ile.老师面带微笑走进教室。二、表示“同时”或“同一方向”,意为“随着”或“与……同时”。例如:The weatherchanges with the tem perature.天气随着温度而变化。W ith these words,the tigerjum ped into the river.说完这些话,老虎便跳入水中。三、表示“手段”和“有形的工具”,意为“用/以/靠……”。例如:They needed to… 相似文献
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吕枫 《开封教育学院学报》1993,(3)
Plot Summary of The Scarlet Letter: The Scarlet Letter has as its setting Puritan Boston during the mid-17th century.Young Hester Prynne,a“fallen woman”,is sentenced towear a scarlet A,signifying“adultery,”because she has a lover whenher aged husband is not with her.Consequently she is driven out of theordinary relations with humanity,and is thus able to view critically thevarious aspects of the society.Hester is not overwhelmed by the harsh 相似文献
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The supercontinuum （SC） generation at the repetition rate of 10 GHz is presented. The SC is generated in a 4.2 km conventional dispersion-shifted fiber （ DSF）, which is produced with nonlinear effects and group velocity dispersion. The DSF is pumped by an actively mode-locked Er^3＋ -doped fiber laser with pulse width of 7. 97 ps. A novel SC pulse source with a bandwidth up to 125 nm is obtained, which covers the whole C, L bands and part of S band. The stable, narrow pulses with mean pulse-width of 9.7 ps and time-bandwidth product of 0. 48 are filtered out across the whole SC bandwidth. This supercontinuum pulse source is suitable for future high-speed optical communications. 相似文献
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Algorithm for 2D irregular-shaped nesting problem based on the NFP algorithm and lowest-gravity-center princlple 总被引：1，自引：0，他引：1
LIU Hu-yao HE Yuan-jun 《浙江大学学报(A卷英文版)》2006,7(4):570-576
The nesting problem involves arranging pieces on a plate to maximize use of material. A new scheme for 2D irregular-shaped nesting problem is proposed. The new scheme is based on the NFP （No Fit Polygon） algorithm and a new placement principle for pieces. The novel placement principle is to place a piece to the position with lowest gravity center based on NFP. In addition, genetic algorithm （GA） is adopted to find an efficient nesting sequence. The proposed scheme can deal with pieces with arbitrary rotation and containing region with holes, and achieves competitive results in experiment on benchmark datasets. 相似文献
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The hippopotamus is a big animal. It feeds on plants. It is a hoofed mammal. It has thick, hairless skin, short legs and a large head with an enormous mouth.The hippopotamus is found in and near lakes and rivers in tropical Africa . The Africans call it 'River Horse'. It swims about with its whole body under water, but it keeps its eyes and nostrils above the water at all times. It does this to breathe and look around while it is swimming. 相似文献
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《海外英语》2008,(10):17-18
1 As the first film to re-create the 208 A.D. Battle of Chibi, themost famous military feat in Chinese history, John Woo's "RedCliff" is a Pan-Asian project with the word "monumental" written allover it. The 140-minute first half that opened across major Asianterritories is only a prelude that provides the beams and columns forthe narrative framework, but with a few decisive and spot-on actionspectacles, it sufficiently kindles expectations for the climactic clash inupcoming Part 2.…… 相似文献
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The co-effect of transmitted power fluctuation and system nonlinearity produce deviations in scatterometer measurement results . An internal calibration method to deal with this problem is proposed. The method can result in more precise scatterometric measurements in a wide range. The basic principle of the method is combining real-transmitted-power detection with the calibration of system nonlinearity. A practical scheme to implement the method is also presented, which is developed based on a special designed mechanism of a microwave radiometer-scatterometer combined system. 相似文献
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Two numerical simulations were performed to investigate the protective effect of the foam cladding. One simulation is based on a previous experimental study, which is a ballistic pendulum with and without a foam cladding subjected to close-range blast loading. The other model is a steel beam with and without a foam cladding under blast loading. The overpressure due to the blast event can be calculated by the empirical function ConWep or by an arbitrary Lagrangian-Eulerian (ALE) coupling model. The first approach is relatively simple and widely used. The second approach can model the propagation of the blast wave in the air and the interaction between the air and the solid. It is found that the pendulum with the foam cladding always swings to a larger rotation angel compared to a bare pendulum. However, the steel beam with an appropriate foam cladding has a smaller deflection compared to the bare beam without a foam cladding. It is concluded that the protective effect of the foam cladding depends on the properties of the foam and the protected structure. 相似文献
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MA Guowei YE Ziqing ZHANG Xingui 《天津大学学报(英文版)》2006,12(B09):122-125
Two numerical simulations were performed to investigate the protective effect of the foam cladding. One simulation is based on a previous experimental study, which is a ballistic pendulum with and without a foam cladding subjected to close-range blast loading. The other model is a steel beam with and without a foam cladding under blast loading. The overpressure due to the blast event can be calculated by the empirical function ConWep or by an arbitrary Lagrangian-Eulerian （ALE） coupling model. The first approach is relatively simple and widely used. The second approach can model the propagation of the blast wave in the air and the interaction between the air and the solid. It is found that the pendulum with the foam cladding always swings to a larger rotation angel compared to a bare pendulum. However, the steel beam with an appropriate foam cladding has a smaller deflection compared to the bare beam without a foam cladding. It is concluded that the protective effect of the foam cladding depends on the properties of the foam and the protected structure. 相似文献
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This paper models a low-power high-frequency digitally controlled synchronous rectifier （SR） OUCK converter. The converter is a hybrid system with three operation modes. Digital PID controler is used. Key problems such as quantization resolution of digital pulse-width modulation （DPWM） and steady-state limit cycles of digital control switching model power supply （SMPS） are discussed, with corresponding solutions presented. Simulation of a digital control synchronous buck is performed with a fixed-point algorithm. The results show that the described approach enables high-speed dynamic performance. 相似文献
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The dynamic response of moored crane-ship is studied. Governing equations for the dynamic response of a crane-ship coupled with the pendulum motion of the payload are derived based on Lagrange＇s equations. The boom is modeled based on finite element method, while the payload is modeled as a planar pendulum of point mass. The dynamic response was studied using numerical method. The calculation results show that the large-amplitude responses occur at wave periods near the natural period of the payload. Load swing angle is smaller for crane-ship with flexible boom, in comparison with rigid boom. The ship surge motions have large vibrations for crane-ship with flexible boom, which were not observed for a rigid boom. The analysis identifies the significance of key parameters and reveals how the system design can be adjusted to avoid critical conditions. 相似文献
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This paper presents an investigation of inverter fault-tolerant operation for a permanent magnet synchronous motor （PMSM） direct torque control （DTC） system under various inverter faults. The performance of a faulty standard 6-switch inverter driven PMSM DTC system is analyzed. To avoid the loss or even disaster caused by the inverter faults, a topology-modified inverter with fault-tolerant capability is introduced, which is reconfigured as a 3-phase 4-switch inverter. The modeling of the 4-switch inverter is then analyzed and a novel DTC strategy with a unique nonlinear perpendicular flux observer and feedback compensation scheme is proposed for obtaining a continuous, disturbance-flee drive system. The simulation and experimental results demonstrate that the proposed inverter fault-tolerant PMSM DTC system is able to operate stably and continuously with acceptable static and pretty good dynamic performance. 相似文献
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"The Old Man and The Sea"is Hemingway latter years’masterpiece,with which he was awarded the Nobel prize in1954.As the protagonist of the novel,Santiago plays a vital role to the novel’s motif.Hemingway expresses his attitudes toward the life through the image of Santiago.The paper intends to explore the character of Santiago from different facets and angles.In the end,we reach a conclusion that Santiago is a strong-willed man with a young,indestructible soul,he is kind,sensitive as well as hardworking.In a ward,he is a perfect Hemingway hero. 相似文献
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The purpose of this study was to build a flexible mechanical system with a hydrostatic skeleton. The main components of this system are two type flexible bags. One is a structural bag with constant inner pressure. The other is an actuator bag with controlled inner pressure. To design the system, it was necessary to estimate both structural deformation and driving force. Nu- merical analysis of flexible bags, however, is difficult because of large nonlinear deformation. This study analyzed structural strength and driving force of flexible bags with the nonlinear finite element analysis （FEA） software ABAQUS. The stress con- centration dependency on the bag shape is described and the driving force is calculated to include the large deformation. From the analytical results, this study derives an empirical equation of driving force. The validity of the equation was confirmed by condition-changed analyses and experimental results. 相似文献
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Modified surface tension model for free surface flow with single-phase lattice Boltzmann method 总被引：1，自引：0，他引：1
A single-phase lattice Boltzmann model with modified surface tension is developed in this paper to solve the problem of high-density-ratio free surface flow.The computational efficiency and accuracy are both enhanced.The restriction to the relaxation factor （which needs to be smaller than 1） is circumvented by the new surface tension algebra,due to its rational physical nature compared with the treatment of Xing,Buther and Yang in their paper （Comp.Mater.Sci.,2007,39（2）：282-290）.The proposed stable surface tension scheme is applied to simulate the free deformation of a square droplet with surface tension effect and the process of a droplet impinging on a liquid film.The numerical solution for free deformation of a droplet agrees well with thermodynamic principles,and also achieves high accuracy in comparison with Xing,et al.＇s model.Three typical impinging modes are successfully obtained with the new scheme,and another particular mode found by Wang and Chen is also successfully simulated.The evolutions of liquid crown agree well with the power law related to time. 相似文献
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《天津大学学报(英文版)》2010,(2)
The cumulative sum (CUSUM) algorithm is proposed to detect the selfish behavior of a node in a wireless ad hoc network. By tracing the statistics characteristic of the backoff time between successful transmissions, a wireless node can distinguish if there is a selfish behavior in the wireless network. The detection efficiency is validated using a Qualnet simulator. An IEEE 802.11 wireless ad hoc network with 20 senders and 20 receivers spreading out randomly in a given area is evaluated. The well-behaved senders use minimum contention window size of 32 and maximum contention window size of 1 024, and the selfish nodes are assumed not to use the binary exponential strategy for which the contention window sizes are both fixed as 16. The transmission radius of all nodes is 250 m. Two scenarios are investigated: a single-hop network with nodes spreading out in 100 m×100 m, and all the nodes are in the range of each other; and a multi-hop network with nodes spreading out in 1 000 m×1 000 m . The node can monitor the backoff time from all the other nodes and run the detection algorithms over those samples. It is noted that the threshold can significantly affect the detection time and the detection accuracy. For a given threshold of 0.3 s, the false alarm rates and the missed alarm rates are less than 5%. The detection delay is less than 1.0 s. The simulation results show that the algorithm has short detection time and high detection accuracy. 相似文献
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In the present paper,a new image processing method for photocarrierspeckle fringe is proposed.A simple and fast filter is designed for different kinds of specklefringe with certain direction to eliminate the speckle effect.Fringe multiplication is carriedout with personal computer.The procedure of photocarrier speckle image collecting,pro-cessing,calculating and verifying is described with a practical example. 相似文献