川北地形过渡带地形因子对土地利用与景观格局变化的影响

[目的]基于地形特征分析不同用地类型时空分布变化,不仅能解释土地利用时空变化规律,并能更进一步为优化土地利用结果,生态环境保护奠定基础。[方法]基于四川省北部江油市2003,2010,2018年3期遥感影像,运用土地利用转移矩阵法,分析不同用地类型之间的转化情况;接着利用地形位指数法、分布指数法,分析地形因子影响下不同用地类型分布指数变化特征;之后利用移动窗口法,探究景观格局中斑块密度与Shannon多样性指数时空变化规律;最后结合双变量空间相关性分析,分析地形因子与景观指数间的空间相关性特征。[结果](1)在2003—2010年期间,水田面积减少最多(减少面积2 238.98 hm~2),建设用地面积增加最多(面积增加3 360.36 hm~2);在2010—2018年期间,水田面积减少1 175.84 hm~2,建设用地面积增加1 614.78 hm~2;2003—2010年期间江油市土地利用的变化量整体高于2010—2018年。(2)北部山区主要由旱地转移为林草地,南部平原地区主要为水田转移为建设用地,中部丘陵区域旱地和水田相互转化强烈。(3)随时间变化,旱地和未利用地优势等级向中地形位等级靠拢;低地形位等级上建设用地、水田和水域优势度逐渐降低,并具有优势等级向较高地形位等级扩展趋势。(4)山区河流沿岸以及山地平原交汇处斑块密度与Shannon多样性指数较高,且呈线性分布;随时间变化,丘陵区域斑块密度增加,主城区附近Shannon多样性指数呈下降趋势。(5)高—高聚集区主要表现为向山地丘陵交汇处聚集;城区附近景观指数因受其他因素影响较多,导致该区域景观指数与地形位指数呈现出不显著相关性。[结论]在地形过渡带区域,不同地貌对于各类用地变化的影响在时空上存在差异性,其地形因子与景观指数的空间相关性差异明显。     

Land Cover Transition in Northern Tanzania

Land conversion in sub‐Saharan Africa has profound biophysical, ecological, political and social consequences for human well‐being and ecosystem services. Understanding the process of land cover changes and transitions is essential for good ecosystem management policy that would lead to improved agricultural production, human well‐being and ecosystems health. This study aimed to assess land cover transitions in a typical semi‐arid degraded agro‐ecosystems environment within the Pangani river basin in northern Tanzania. Three Landsat images spanning over 30 years were used to detect random and systematic patterns of land cover transition in a landscape dominated by crop and livestock farming. Results revealed that current land cover transition is driven by a systematic process of change dominated by the following: (i) transition from degraded land to sparse bushland (10·8%); (ii) conversion from sparse bushland to dense bushland in lowland areas (6·0%); (iii) conversion from bushland to forest (4·8%); and (iv) conversion from dense bushland to cropland in the highlands (4·5%). Agricultural lands under water harvesting technology adoption show a high degree of persistence (60–80%) between time slices. This suggests that there is a trend in land‐use change towards vegetation improvement in the catchment with a continuous increase in the adoption of water harvesting technologies for crop and livestock farming. This can be interpreted as a sign of agricultural intensification and vegetation regrowth in the catchment. Copyright © 2015 John Wiley & Sons, Ltd.     

小江流域土地利用变化及其趋势分析

运用遥感和地理信息系统技术，提取了小江流域1987，1995年和2000年土地利用空间数据，分析了1987～2000年间小江流域土地利用类型变化的幅度、速度以及类型之间相互转移，并应用马尔柯夫概率模型对小江流域2015年土地利用格局进行了预测。结果表明：13年来小江流域耕地、林地以及城乡工矿用地面积均显著增加，其中耕地增加最为显著，由1987年的345．1km^2增加到2000年的398．7km^2。小江流域土地利用变化速度很快，年均变化速度达0．49％；对单一土地利用类型来说，城乡工矿用地的年均变化速度最大，年变化率达3．52％，其次为耕地和水域。增加的耕地主要来自草地、林地和水域；林地中除部分转化为耕地外，由12．64％的林地退化成草地；草地和未利用地基本保持不变。到2015年，小江流域耕地、林地、水域和城乡工矿用地面积和比例将会增加，草地和未利用地面积和比例将会下降。     

线粒体与细胞凋亡

细胞凋亡是一种由基因控制的细胞自杀性死亡过程,是机体维持自身稳定的一种基本生理机制。机体通过细胞凋亡清除损伤、衰老与突变的细胞,维持生理平衡。通过对细胞凋亡的研究发现,线粒体在调节细胞凋亡中发挥着关键作用。尤其是被称为细胞凋亡主开关的线粒体通透性改变孔(MitochondrionPermeabilitytransitionPore,MPTP),它是细胞色素C、Smac、AIF等凋亡诱导因子的主要来源。本文以MPTP的开放、细胞色素C、AIF在细胞凋亡中的作用以及Bcl-2家族对细胞凋亡的调控做一综述,以便广大读者能系统地了解线粒体在细胞凋亡中的作用。     

农村投融资制度变迁的经济效应

我国现有农村投融资的糊度性缺陷已成为糊约解决“三农”问题的瓶颈，不适应农业和农村经济发展的需要。文中以翩度经济学为理论依据，分析了农村投融资制度演进的特征，并对其制度变迁的经济效应进行了理论和实证分析。     

一种基于小波变换的图像过渡区提取及分割方法

具有复杂背景的树木图像的分割对于精确对靶施药及智能化植保机械的设计具有重要意义。为实现树木图像的精确分割,针对该类图像的特点,该文提出了一种基于小波变换的过渡区提取树木图像分割方法。通过对比小波变换系数、小波变换系数聚类以及小波包系数,最终选取了同时能够分解出更多高频、低频信息的小波包变换系数提取特征,根据小波包变换系数定义了小波能量比参数,将小波能量比参数值归一化为图像灰度值,采用自适应阈值和神经网络两种方法提取了过渡区,实现了具有复杂背景树木图像的分割。试验表明,该方法分割精度高,对于分割复杂背景的树木图像具有特别意义。     

温度与膜脂脂肪酸对不同抗冷性玉米幼苗ATP酶的影响

我们以抗冷性不同的玉米幼苗（１—４级，抗冷性递减）为材料，研究了其线粒体ＡＴＰ酶在１１℃、２４℃的活力、温度变化时其活化能（Ｅａ）的突变温度以及线粒体膜脂脂肪酸组成。结果表明在１１℃条件下，ＡＴＰ酶活力随品种抗冷性增加而增强；酶活化能折，点温度随品种抗个性增加而降低，脂肪酸的不饱和指数随品种抗个性增加而增大。这说明膜脂不饱和度控制着ＡＴＰ酶的活力，Ｅａ的折点温度受膜流动性的影响并与品种抗冷性有关，我们认为ＡＴＰ酶Ｅａ的折点温度可作为玉米幼苗抗个性生化指标。另外通过玉米幼苗抗冷性锻炼表明：ＡＴＰ酶Ｅａ折点温度没变化，说明幼苗抗冷潜力很小。     

Glass transition behavior of corn distillers dried grains with solubles (DDGS)

Distillers dried grains with solubles (DDGS), a major co-product from the corn ethanol industry, has high feed value for its chemical composition. The ratio of wet distillers grains (WDG) and condensed distillers solubles (CDS) added during the production process determines the chemical composition of DDGS. Effect of changing this ratio and the influence of moisture content on glass transition behavior of DDGS was studied. Five prediction models were evaluated to explain the glass transition of DDGS. The mixed trends in the result indicated the complex behavior of DDGS particles and revealed that both moisture content and chemical composition impact the glass transition behavior of DDGS. Onset glass transition temperature ranged from 20 to 30 °C depending on the chemical composition. Kwei equation predictions were better than the predictions by Gordon-Taylor equation. The glass transition temperature of DDGS can be mathematically explained by combining the moisture content and chemical components protein, fiber, glycerol, and sugar percent. The artificial neural network (ANN) model gave a better prediction of onset and midpoint glass transition temperature of DDGS and this might be due to the accurate mapping of the interaction between chemical components.     

Frozen bread dough: Effects of freezing storage and dough improvers

This review focuses on the effects of freezing storage on the microstructure and baking performance of frozen doughs, and provides an overview of the activities of dough improvers, including emulsifiers, hydrocolloids and other improvers used in frozen dough applications. The overall quality of bread baked from frozen dough deteriorates as the storage of the dough at sub-zero temperatures increases due to several factors which are discussed. Lipid-related emulsifiers such as diacetyl tartaric acid esters of mono and diglycerides and sucrose esters employed as anti-staling agents, dough modifiers, shortening sparing agents, and as improvers for the production of high-protein bread have also been employed in frozen doughs. Hydrocolloids are gaining importance in the baking industry as dough improvers due to their ability to induce structural changes in the main components of wheat flour systems during breadmaking steps and bread storage Their effects in frozen doughs is discussed. Other dough improvers, such as ascorbic acid, honey and green tea extract, are also reviewed in the context of frozen doughs.     

Rapid Economic Change,the Nutrition Transition and Its Effects on the Structure of Consumption: The Nutrition Transition in China

SUMMARY

Economic, demographic, and technological changes have led to a marked shift in the diet structure and the distribution of body composition in many regions of the world. Such changes include rapid reduction in fertility and aging of the population, urbanization, epidemiological transition, and the uneven distribution of the effect of economic reform. Research presented for China shows that it is undergoing a marked shift in its diet, activity, and nutritional status patterns. This paper presents data on the shifts in the structure of food decision-making and the associated body composition shifts.