使用新型延时器件的星/三角起动线路

船舶电网需要有效地控制起动电流 ,本文讨论了一种使用新型延时器件的星 /三角起动线路 ,该线路能够可靠地完成星形线路到三角形线路的转换 ,抑制“飞弧短路”

三相异步电动机在低负载率下节能控制

根据电机在工矿企业应用的现状,首先分析了三相异步电动机的负载率越低与对应的功率因数越低的相互关系,并提出在电动机低负载率下通过三角形连接转换成星形连接的降压方式来提高其电机的功率因数;其次分析了三相异步电动机负载率越低与其对应的效率也越低的关系,在低负载率下电动机的星形连接的效率要高于三角形连接的效率,并近一步分析了在电机低负载率下星形与三角形切换点的电流数值的计算;最后还分析了根据电动机的星/三角不同工作状态下采用并联相应电容量来提高功率因数,达到了三相异步电动机在低负载率的节能控制目标。

Approximate Approaches to Geometric Corrections of High Resolution Satellite Imagery

The exploitation of different non-rigorous mathematical models as opposed to the satellite rigorous models is discussed for geometric corrections and topographic/thematic maps pro duction of high-resolution satellite imagery (HRSI). Furthermore, this paper fo cuses on the effects of the number of GCPs and the terrain elevation difference within the area covered by the images on the obtained ground points accuracy. Fr om the research, it is obviously found that non-rigorous orientation and triang ulation models can be used successfully in most cases for 2D rectification and 3 D ground points determination without a camera model or the satellite ephemeris data. In addition, the accuracy up to the sub-pixel level in plane and about on e pixel in elevation can be achieved with a modest number of GCPs.

Impacts of Land Use and Cover Change on Land Surface Temperature in the Zhujiang Delta

Remote sensing and geographic information systems (GIS) technologies were used to detect land use/cover changes (LUCC) and to assess their impacts on land surface temperature (LST) in the Zhujiang Delta. Multi-temporal Landsat TM and Landsat ETM+ data were employed to identify patterns of LUCC as well as to quantify urban expansion and the associated decrease of vegetation cover. The thermal infrared bands of the data were used to retrieve LST. The results revealed a strong and uneven urban growth,which caused LST to raise 4.56℃in the newly urbanized part of the study area. Overall, remote sensing and GIS technologies were effective approaches for monitoring and analyzing urban growth patterns and evaluating their impacts on LST.

Cultivated Land Changes and Their Driving Forces——A Satellite Remote Sensing Analysis in the Yellow River Delta,China

Taking Kenli County in the Yellow River Delta, China, as the study area and using digital satellite remote sensing techniques, cultivated land use changes and their corresponding driving forces were explored in this study. An interactive interpretation and a manual modification procedure were carried out to acquire cultivated land information. An overlay method based on classification results and a visual change detection method which was supported by land use maps were employed to detect the cultivated land changes. Based on the changes that were revealed and a spatial analysis between cultivated land use and related natural and socio-economic factors, the driving forces for cultivated land use changes in the study area were determined.The results showed a decrease in cultivated land in Kenli County of 5321.8 ha from 1987 to 1998, i.e.,an average annual decrement of 483.8 ha, which occurred mainly in the central paddy field region and the northeast dry land region. Adverse human activities, soil salinization and water deficiencies were the driving forces that caused these cultivated land use changes.

Trends of Tropospheric Ozone over China Based on Satellite Data(1979-2005)

Long-term trends of yearly and seasonal averages of tropospheric ozone over the whole country and some important regions of China during 1979-2005 are analyzed,based on tropospheric ozone residue(TOR) data retrieved from satellite measurements.The relationship between the TOR and Southern Oscillation Index(SOI) is studied.The results show that,over the whole country,there is a slight increase of TOR in summer and a decrease in other seasons,while the overall trend for the whole period is insignificant.There are decreasing trends of TOR over the Pearl River Delta and the Sichuan Basin.Significant increasing trends of TOR are found over the North China Plain(NCP) for all seasons except for winter,with a maximum rate of 1.10 DU per decade for summer.There are significant correlations between TOR and SOI for some regions in China but not for the NCP,suggesting that the observed increasing trend of TOR over the NCP may not be linked with changes in atmospheric circulations.

MONITORING THE DIFFUSION OF SUSPENDED SEDIMENTS AND STABILITY OF TIDAL RADIAL SAND RIDGES AREA USING MULTI-SATELLITE REMOTE SENSING DATA

Nine Landsat TM tapes and images and MSS images, 10 NOAA tapes and images and 1 SAR image from 1973 to 1997 were used to analyze the diffusion of suspended sediments and the change of tidal radial sand ridges in the northern part of the Changjiang River delta, the South Yellow Sea. The results showed that the diffusion of suspended sediments was controlled by the tide, net current, and submarine topography in this area. The distribution of suspended sediments had close relationship with the submarine topography. The old Huanghe River delta and the Changjiang River comprise the main sediment supply for the formation of radial sand ridges, whose evolution can be divided into three stages since the Huanghe River changed its course and flowed northward into the Bohai Sea.

Heteroclinic and Homoclinic Connections between the Sun-Earth Triangular Points and Quasi-Satellite Orbits for Solar Observations

Investigation of new orbit geometries exhibits a very attractive behavior for a spacecraft to monitor space weather coming from the Sun. Several orbit transfer mechanisms are analyzed as potential alternatives to monitor solar activity such as a sub-solar orbit or quasi-satellite orbit and short and long heteroclinic and homoclinic connections between the triangular points L4 and L5 and the collinear point L3 of the CRTBP （circular restricted three-body problem） in the Sun-Earth system. These trajectories could serve as channels through where material can be transported from L5 to L3 by performing small maneuvers at the departure of the Trojan orbit. The size of these maneuvers at L5 is between 299 m/s and 730 m/s depending on the transfer time of the trajectory and does not need any deterministic maneuvers at L3. Our results suggest that material may also be transported from the Trojan orbits to quasi-satellite orbits or even displaced quasi-satellite orbits.