东北三省土地利用及生境质量的时空演变效应

探究东北三省土地利用及生境质量的时空演变效应,对东北三省生态环境保护和区域高质量发展具有重要意义。基于此,该文选取东北三省2000、2005、2010、2015、2018年的土地利用分类数据,按照土地利用的“三生”功能分类,分析东北三省2010-2018年土地利用和生境质量的时空变化特征,结果表明:(1)2000-2018年间东北三省土地利用格局上存在显著差异;土地利用类型转变显著,其中农业生产用地增幅最为明显,达10604.28 km^(2),用地面积减少最为明显的是林业生态用地,总计减少了19400.4 km^(2)。(2)2000-2018年间东北三省生境质量等级整体上呈现下降趋势,低等水平生境质量区域面积持续扩张,增幅达到19369 km^(2);中等生境质量区域也在扩张,其面积增加了20807 km^(2);而生境质量良好和生境质量优等的区域面积分别减少了19991 km^(2)、10185 km^(2)。(3)生境质量空间分布与土地利用类型分布关系密切,生境质量水平高的区域多位于林地与草地生态空间广布的区域,而生境质量低的地区其生活空间与生产空间占比较高。

“淘宝村”电商生产空间演变效应及优化--以山东省曹县大集镇丁楼村为例

以中国首批20个“淘宝村”之一的山东省曹县大集镇丁楼村为研究案例,借助参与式农户调查法和空间分析方法,分析电商生产空间的演变及其效应,并提出优化策略。结果表明:(1)在“淘宝村”发展过程中,农户尺度电商产业发展依次经历家庭作坊主导阶段、独立作坊兴起阶段和现代工厂兴起阶段,生产空间外部形态现代性增强,内部格局逐步独立,各功能空间专业分工更加明确。(2)村域尺度电商生产空间在村内集聚发展的同时,不断向村外道路便利处迁移。电商生产空间分布具有明显的规模指向和道路交通指向。(3)信息化为转型国家乡村经济发展与城乡关系改善提供新的可能性,提高了乡村年轻化水平和家庭劳动生产率。但是,住房“空废化”与电商生产空间紧缺现象并存于“淘宝村”,农村土地利用制度创新和乡村振兴规划支撑作用需要对此做出有效应对。

人类活动影响下的钱塘江河口环境演变初探

钱塘江河口是强潮喇叭状河口,其演变既受到自然因素的制约,又受到人类活动的强烈影响。诸如修筑堤坝、围垦造陆等一系列工程措施改变了河口水动力、沉积和地貌特征,使得人类活动影响逐渐加强,自然影响因素退居次要位置,河口的自动调整作用亦随之减弱。通过分析河口主要自然特征,根据近几十年来大规模人类活动过程及其对河口的影响,研究河口演变特征对人类活动的响应及其发展趋势。研究结果表明:潮滩围垦和江道缩窄等工程措施稳定河口区主槽,加快河道延长,不同河段因过水断面改变而使潮流量变化各异,但总潮位并未减弱,且有所抬高;河口持续淤积,河口沙坎受季节影响呈现"洪冲枯淤"的变化,且位置总体下移;河口喇叭状地貌形态日益突出,口门位置不断向外海延伸。

资产结构演变的熵值有序性研究——以我国煤炭上市公司为例

企业资产结构演变是否体现有序性,这种有序性能否给企业带来正效应,是本研究的目的。以我国煤炭上市公司为例,收集煤炭上市公司1998—2017年20年数据,采用熵值法计算熵值。结果表明:1998-2017年我国煤炭上市公司占资产总额主体地位的流动资产占比和固定资产占比呈下降趋势,但熵值充分体现了资产结构演变的有序性。这种有序性演变提升了企业经营资产收入率,推进了企业创利水平不断上升,伴生了煤炭企业科技水平的不断提高,煤炭企业未来应在资产结构有序演变及其效应上把控经营资产发展的主体方向。

Microstructure and superhardness effect of VC/TiC superlattice films

Vanadium carbide/titanium carbide （VC/TiC） superlattice films were synthesized by magnetron sputtering method. The effects of modulation period on the microstructure evolution and mechanical properties were investigated by EDXA, XRD, HRTEM and nano-indentation. The results reveal that the VC/TiC superlattice films form an epitaxial structure when their modulation period is less than a critical value, accompanied with a remarkable increase in hardness. Further increasing the modulation period, the hardness of superlattices decreases slowly to the rule-of-mixture value due to the destruction of epitaxial structures. The XRD results reveal that three-directional strains are generated in superlattices when the epitaxial structure is formed, which may change the modulus of constituent layers. This may explain the remarkable hardness enhancement of VC/TiC superlattices.

Spatial acoustic emission evolution of red sandstone during multi-stage triaxial deformation

Multi-stage triaxial compression tests for cylindrical red sandstone specimens(diameter of 50 mm,height of 100 mm) were carried out with a rock mechanics testing system and spatial acoustic emission(AE) locations were obtained by adopting an AE monitoring system.Based on spatial AE distribution evolution of red sandstone during multi-stage triaxial deformation,the relation between spatial AE events and triaxial deformation of red sandstone was analyzed.The results show that before peak strength,the spatial AE events are not active and distribute stochastically in the specimen,while after peak strength,the spatial AE events are very active and focus on a local region beyond final microscopic failure plane.During multi-stage triaxial deformation with five different confining pressures,the spatial AE distribution evolution in the red sandstone was obtained.The obtained spatial AE locations of red sandstone at the final confining pressure agree very well with the ultimate failure experimental mode.Finally,the influence of confining pressure on the spatial AE evolution characteristics of red sandstone during triaxial deformation was discussed.The AE behavior of red sandstone during multi-stage triaxial deformation is interpreted in the light of the Kaiser effect,which has a significant meaning for predicting the unstable failure of engineering rock mass.

Deformation behaviour and microstructure evolution of AlMg6Mn alloy during shear spinning

Deformation behavior and microstructure of AlMg6Mn alloy subjected to shear spinning were studied by means of mechanical characterization, optical and SEM＋EDS microscopy. Specimens were shear spun on an industrial spinning machine using different mandrels, providing reductions of wall thickness of 30%, 50% and 68%. The grain structure developed during shear spinning refines gradually. The grains elongate in axial direction with increase of reduction, and also stretches along circumferencial direction. Optimal combination of strength and elongation is observed. This is attributed to grain refinement and dislocation reactions with particles and atoms of Mg and Mn in solid solution.

Effects of electric field fringe on performances of grid strip capacitive MEMS devices

Sensing structure of grid strip capacitors can be used in the design of capacitive micro-electromechanical system （MEMS） resonators, accelerometers etc. A grid strip structure consists of nonentirely overlap plates so that the capacitor fringe effect cannot be neglected in the design. Electricmagnetic Finite Element Method （FEM） software ANSOFF-Maxwell is employed to analyze the fringe effect of a grid strip capacitor. The analysis includes capacitance changes with change of overlap length, overlap width, plate thickness, grid strip density etc. The results show that fringe effect leads to non-linear change of grid strip capacitance with the change of overlap length and width, that the capacitance increases with the increase of grid strip width and plate thickness, and that sensitivity can be improved through the increase of grid strip density in the condition of identical total overlap area, but linearity is reduced.

Change in Urban Wetlands and Their Cold Island Effects in Response to Rapid Urbanization

The cold-island effect of urban wetlands has received increasing attention in recent years due to its important role in the alleviation of urban heat islands.Hangzhou,a representative rapidly urbanizing city with rich wetlands in China,was selected as a case study for researching the changes that the urban wetlands have undergone and their impact on the urban thermal environment.Land surface temperature(LST) was acquired from the thermal infrared data of Landsat 5 Thematic Mapper(TM) images in 1990,1995,2000,2006,and 2010,using the single-channel method.The results are as follows:1) considering the changes in land use,the urban wetlands located to the west of Hangzhou have decreased significantly during 1990–2010 because of rapid urbanization.In the Xixi Wetland,the change in land use was relatively small and most of the water body and vegetation were preserved.However,to the east of the Xixi Wetland,large areas of water body and vegetation have been replaced by built-up land as a result of the urbanization process;2) considering the change in LST,it was found from land surface temperature retrieval that the changing spatial pattern of the thermal field was highly correlated with land use changes.Low temperature regions of the eastern Xixi Wetland were gradually eroded by high temperature regions,and the centroid of the heat island in East Xixi was found to be constantly shifting westward.In addition,the difference in LST between the Xixi Wetland and East Xixi has increased;3) considering the impact factors for this area,land use structure and patch shape were found to have a significant impact on LST,shown by the results of multiple linear stepwise regressions.Increasing the size of the wetlands in urban planning is considered to be the most effective measure in alleviating the urban heat island effect.Moreover,reducing the spatial complexity of landscape patches also contributes to the alleviation of the urban heat island effect.

Evolution and Effects of the Social-ecological System in Karst Mountainous Regions:A Case Study of Guangxi,China

Karst regions are the typical areas of interaction between human society and natural ecosystems.Understanding the historical mechanisms of the evolution of social-ecological systems(SES)is crucial for the future sustainable management of karst regions.This study selected Guangxi,a typical karst mountainous region in Southwest China,as the study area,and used population,cropland area,and forest coverage as the SES elements.Based on the framework of SES research in the karst region,it adopted segmented linear regression to identify the stages of the interactions among these elements,to reveal the evolutionary stages of social development from the long-term perspective.In addition,the driving factor indicators were constructed from the aspects of natural environment,social development,government policy,and climate change,and then the feedback changes brought about by the evolution were investigated.The results show that the evolution of SES in Guangxi from 1363-2020 can be divided into seven stages.In the first,second,and early period of the third stages,the government of Guangxi mainly focused on agricultural activities,although the only way to meet the growing demand for food was by expanding the area of cropland,and the timber trade’s pursuit of economic development,resulting in an increase in rocky desertification.In the fourth stage,the ecological environment improved under the implementation of measures such as the control of rocky desertification and the compensation of forest ecological benefits.After the fifth stage,the effect of rocky desertification control has been remarkable.Although the implementation of relevant policies has alleviated the environmental problems to some extent,the continual changes in the structure and function of SES can challenge further progress towards sustainability in karst regions.This study aims to provide a reference for the long-term national spatial planning and the development of environmental policies in karst regions.

The Indian monsoonal influence on altitude effect of δ^(18)O in surface water on southeast Tibetan Plateau

The altitude effect of δ18O is essential for the study of the paleo-elevation reconstruction and possible to be solved through modern process studies. This study presents new δ18O results from southeast Tibetan Plateau along two transects, the Zayu transect and the Lhasa-Nyang transect, with δ18O data from June to September representative of monsoon period and δ18O data during the rest of the year of non-monsoon period. Altitude effect outweighs the longitude and latitude effects in determining regional δ18O variation spatially. Relevant δ18O data from previous studies in the nearby region have also been combined to comprehensively understand the influence of different moisture sources on δ18O from local scale to regional scale. The δ18O in surface water in the southeast Tibetan Plateau and its nearby regions influenced by the Indian summer monsoon shows that single dominant moisture source or simple moisture sources lead to smaller altitudinal lapse rate, whilst growing contributions from local convection to precipitation enlarge δ18O-altitude rate. It thereupon reveals the significance of the Indian summer monsoon to the altitude effect of δ18O in surface water, and the complicated effect of local convection or westerlies evolution to the variation of altitudinal lapse rate. Paleo-monsoon evolution therefore should be considered when altitude effect is applied to paleo-elevation reconstruction for the Tibetan Plateau.

Effects of temperature on the dynamic evolution of two-photon photorefractive screening spatial solitons

We investigate theoretically the temperature effects on the evolutions of both bright and dark screening spatial solitons in biased two-photon photorefractive crystals.For a stable bright or dark two-photon screening spatial soliton originally formed in a crystal at a given temperature,when the crystal temperature changes,it will evolve into another stable screening soliton if the temperature change is quite small,while it will become unstable or break down if the temperature change is large enough.The spatial shape of a stable two-photon screening spatial soliton can be changed by appropriately adjusting the crystal temperature.