A quantitative investigation of the uncertainty associated with mapping scale in the production of land-cover/land-use data

ABSTRACT

Mapping scale is an essential issue in land use and land cover (LULC) data production, which always involves the minimum mapping unit (MMU) that stipulated in the product specification. Since the application of MMUs will inevitably cause some inappropriate classification problems, a technique is needed to evaluate the impact on the data outputs. In this study, a novel method is proposed to investigate the classification uncertainty brought by MMUs on LULC data. The omission errors are predicted based on an assumption of the skewed frequency distribution of the LULC patch size, and the commission errors are subsequently computed through the conversion possibilities among different land classes, which can be deduced from the generalization rule. A test is conducted on real data to verify the underlying assumption on the patch size distribution, and the accuracy of the prediction of omission errors is evaluated through a simulation experiment. A case study is also presented to demonstrate the efficiency and feasibility of the proposed method. At the end of this article, the advantages and notes of this method are discussed for further study and application.     

Asymptotic stability of digitally redesigned control systems

This paper analyses an asymptotic stability of a digitally redesigned control system when the states of the analogue and the digital control systems are approximately matched at every sampling point. The digital redesign is a simple method of converting a given analogue controller to an equivalent digital controller in the sense of state-matching. The concerned state-matching technique is to minimise the norm distance between the discretised closed-loop system matrix of linear analogue control system and that of linear digital control system. It is shown that (i) there exists an upper bound of the norm distance to guarantee the asymptotic stability of the digitally redesigned control system and (ii) the trajectories of the linear analogue and the linear digital control systems coincide at every sampling point if the norm distance is zero. Also, a robustness result is provided in the case that nonlinear perturbations occur in the analogue and the digital control systems. Moreover, design conditions for the developed stability analysis are proposed in terms of linear matrix inequalities.     

Majorisations for the eigenvectors of graph-adjacency matrices

We develop majorisation results that characterise changes in eigenvector components of a graph's adjacency matrix when its topology is changed. Specifically, for general (weighted, directed) graphs, we characterise changes in dominant eigenvector components for single- and multi-row incrementations. We also show that topology changes can be tailored to set ratios between the components of the dominant eigenvector. For more limited graph classes (specifically, undirected, and reversibly-structured ones), majorisations for components of the subdominant and other eigenvectors upon graph modifications are also obtained.     

Characteristics and causes of vegetation variation in the source regions of the Yellow River,China

The eco-environment in the source region of the Yellow River in western China has been experiencing deterioration in the past decades. Vegetation affected by climate variables and anthropogenic activities is indicative of eco-environment well-being. To quantify temporal and spatial variations of vegetation coverage and analyse potential causes for the variations, we analysed the normalized difference vegetation index (NDVI), temperature and precipitation data from 2000 to 2007. We found that altitude and topographic aspects have a strong influence on vegetation coverage. Altitudes between 4500 and 4800 m and shady aspects provide more favourable environments for vegetation growth. Data show stronger vegetation growth within the temperature range of 4.5–5.5°C. Vegetation growth generally increases with precipitation. At higher elevations of 4800–5200 m, however, despite high precipitation rates, lower temperatures restrict growth. Local hydrology conditions are found to directly influence vegetation variations. Vegetation degradation increases with distance from surface water boundaries up to 4 km, but groundwater might serve as a reliable source for preventing vegetation from degrading. Finally, we found that the percentage of degradation decreases with increasing distance from residential loci up to 24 km, which suggests that overgrazing can be a lead cause for localized vegetation degradation. Findings of this study may have a broad implication in assessing vegetation variation and grassland restoration.     

HTPB 基浇注PBX 炸药固化反应动力学研究

为研究端羟基聚丁二烯(hydroxyl-terminated polybutadiene,HTPB)基浇注PBX炸药的固化反应特性确定其固化工艺参数,采用非等温DSC法研究HTPB基浇注PBX炸药粘接剂体系固化反应动力学.分别测试升温速率为5、10、15、20 K/min时的DSC数据,得出固化反应动力学方程,计算不同温度下的反应速率常数,绘制固化速率(dα/dt)～固化度(α)关系曲线,并给出常用HTPB基浇注固化炸药的固化温度范围.结果表明:相同固化度条件下,升温速率越大,固化反应速率越大,当固化度达到0.5时,固化反应速率达到最大值,此后逐渐降低,直至为零.     

大尺寸气孔微结构光纤在光纤光栅中的应用

将微结构光纤分为光子晶体光纤和大尺寸气孔微结构光纤两种。详细介绍了大尺寸气孔微结构光纤。其包层的气孔硅结构（或者聚合物硅结构）影响了包层模式的空间分布以及包层模式的有效折射率，使其表现出与传统光纤不同的光学特性。基于这种微结构光纤的光纤光栅对外部折射率的变化显示了很好的稳定性。偏振特性（对长周期光纤光栅）可以大大加强。基于聚合物硅包层的长周期光纤光栅显示了优良的温度调谐性能。     

脉冲激光放大器双程放大特性的理论研究

本文从建立脉冲激光器双程放大输运方程出发,理论上研究了双程放大输出脉冲特性。导出了输入脉冲持续时间t_p小于双程放大间隔时间t_o条件下双程放大过程的瞬态解和能量增益系数公式。在相同输入脉冲能量下,双程放大能量增益系数随t_p的增加或t_o的减小而下降。双程放大同单程放大比较结果表明,在小信号脉冲输入下,双程放大接近于具有两倍增益介质长度的单程放大。而在强饱和时,则相当于具有相同增益介质长度的单程放大。     

基于体素模型与卷积神经网络的三维模型分类算法

针对传统三维模型分类算法时间复杂度较高、分类准确率较低等问题,提出一种基于体素模型与卷积神经网络的三维模型分类算法。将原始模型表示为八叉树结构的体素模型以优化模型的性状表达,使用设计的卷积神经网络对体素模型进行特征提取以及分类运算。实验结果表明,与其他三维模型分类算法相比,该分类算法的显存占用较小,同时具有较低的时间复杂度和较高的分类能力。     

集成电路可测性设计IO复用方法

超大规模集成电路特征尺寸逐步缩小的发展过程中,芯片面积是制约芯片成本的最重要因素之一,也是直接影响半导体产品市场竞争力的最重要因素之一。本文介绍了将所有可测性设计(DFT)的输入输出端口(IO)与各种类型的正常功能工作模式的IO复用的方法,从而达到减少IO并最终减小芯片面积的目的。介绍了输入信号和输出信号分别在单向端口IO和双向端口IO中复用的方法。然后,以一款经过0.18μm逻辑工艺流片验证的flash存储器控制芯片为例,对比了采用IO复用方法前后芯片的利用率和面积,证明了方案的可行性和有效性。