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黄河三角洲盐生草甸白茅(Imperata cylindrica var. major)群落季节性动态的研究 总被引:1,自引:0,他引:1
采用定位研究的方法研究了生长季白茅(Imperata cylidrica var. major)群落的主要特征和动态。群落的种类组成较简单,其盖度一般在七月中旬达到100%。群落的高增长及地上生产量符合逻辑斯蒂增长模型(Logistic model),并主要受环境中水分和温度因子的影响。群落的最大高度为59cm,出现在八月中旬;地上生产量最大值为干重563g/m~2,出现在九月中旬。 相似文献
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For a cone-beam three-dimensional computed tomography (3D-CT) scanning system, voxel size is an important indicator to guarantee the accuracy of data analysis and feature measurement based on 3D-CT images. Meanwhile, the voxel size changes with the movement of the rotary stage along X-ray direction. In order to realize the automatic calibration of the voxel size, a new and easily-implemented method is proposed. According to this method, several projections of a spherical phantom are captured at different imaging positions and the corresponding voxel size values are calculated by non-linear least-square fitting. Through these interpolation values, a linear equation is obtained that reflects the relationship between the voxel size and the rotary stage translation distance from its nominal zero position. Finally, the linear equation is imported into the calibration module of the 3D-CT scanning system. When the rotary stage is moving along X-ray direction, the accurate value of the voxel size is dynamically exported. The experimental results prove that this method meets the requirements of the actual CT scanning system, and has virtues of easy implementation and high accuracy. 相似文献
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黄河三角洲是中国最大的三角洲之一。草地是本地区主要自然植被类型。芦苇群落、白茅群落、獐茅群落和盐地碱蓬群落是该草地的4个基本类型。本文研究了它们的性质及其环境因子特征。草地的平均年产草量可达2000kg/hecta。将放牧区与割草区分开、控制放牧的时间和强度、限制牧群的数量以及适宜地造林是合理利用草地资源的重要途径。建立自然保护区对于科学研究、草地生态系统的保护是必要的。 相似文献
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For a cone-beam three-dimensional computed tomography (3D-CT) scanning system, voxel size is an important indicator to guarantee the accuracy of data analysis and feature measurement based on 3D-CT images. Meanwhile, the voxel size changes with the movement of the rotary stage along X-ray direction. In order to realize the automatic calibration of the voxel size, a new and easily-implemented method is proposed. According to this method, several projections of a spherical phantom are captured at different imaging positions and the corresponding voxel size values are calculated by non-linear least-square fitting. Through these interpolation values, a linear equation is obtained that reflects the relationship between the voxel size and the rotary stage translation distance from its nominal zero position. Finally, the linear equation is imported into the calibration module of the 3D-CT scanning system. When the rotary stage is moving along X-ray direction, the accurate value of the voxel size is dynamically exported. The experimental results prove that this method meets the requirements of the actual CT scanning system, and has virtues of easy implementation and high accuracy. 相似文献
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