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231.
In this study, a polysaccharide from Enteromorpha prolifera (EP) was extracted and its effect on maize seedlings under NaCl stress was investigated. Firstly, the components and structure of the EP were determined. We found that EP is a sulfated polysaccharide of high-molecular weight (Mw, 1 840 KDa) heteropolysaccharides and the main monosaccharide is rhamnose. The polysaccharide was applied to explore its effect on the growth of maize seedlings and its defense response under a salt stress. The results show that EP could promote the growth of maize seedlings under the salt stress. In addition, EP was shown able to significantly regulate membrane permeability and adjustment of osmotic substances such as soluble protein, soluble sugar, and proline, antioxidant enzymes containing superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase. Therefore, EP is an effective salt-resistant substance for the growth of maize seedlings under NaCl stress. 相似文献
232.
采用经验模式分解技术研究了从第12到第24太阳活动周黑子面积数据中的Rieger-type周期,以及它们在南北半球上的相位关系。研究发现:(1)Rieger-type周期尺度以及时间尺度在两个半球上是不一样的,从而导致了半球分布的不对称性;(2)平均Rieger-type周期在北半球上的周期长度略大于南半球上的;(3)占主导地位半球的Rieger-type周期的相位不一定是超前的,半球Rieger-type周期尺度相近的也并不一定是相关性强的。 相似文献
233.
234.
Lin He Song Wang Xiao-Jie Xu Roberto Soria Ji-Feng Liu Xiang-Dong Li Yu Bai Zhong-Rui Bai Jin-Cheng Guo Yan-Li Qiu Yong Zhang Ruo-Chuan Xu Ke-Cheng Qian 《天文和天体物理学研究(英文版)》2019,(7)
X-ray emission is an important indicator of stellar activity. In this paper, we study stellar Xray activity using the XMM-Newton and LAMOST data for different types of stars. We provide a sample including 1259 X-ray-emitting stars, of which 1090 have accurate stellar parameter estimations. Our sample size is much larger than those used in previous works. We find a bimodal distribution of the X-ray to optical flux ratio(log(fX/fV)) for G and K stars. We interpret that this bimodality is due to two subpopulations with different coronal heating rates. Furthermore, using the full widths at half maxima calculated from Hα and Hβ lines, we show that these stars in the inactive peaks have smaller rotational velocities. This is consistent with the magnetic dynamo theory that presumes stars with low rotational velocities have low levels of stellar activity. We also examine the correlation between log(fX/fV) and luminosity of the excess emission in the Hα line, and find a tight relation between the coronal and chromospheric activity indicators. 相似文献
235.
针对区域大气污染物排放量与空气质量在时空分布上存在不完全协同、匹配的现象,论文选择SO2、NOX、PM2.5、CO和VOCs作为大气污染物指标,选择气溶胶光学厚度(Aerosol Optical Depth, AOD)表征颗粒物环境空气质量,以武汉市为例,综合应用耦合模型和空间错位指数模型研究2类指标之间的空间非协同耦合规律。主要结论如下:① 武汉市大气污染物排放量与颗粒物空气质量具有不同空间分布特征,大气污染物排放量呈现由城市中心城区向远城区递减的趋势,其中SO2、PM2.5和VOCs的排放具有明显的中心聚集现象,而NOX和CO聚集现象不显著,且与道路分布明显相关;AOD分布具有明显的空间差异性,总体上呈由西北向东南依次递减的趋势。② 武汉市大气污染物排放与颗粒物空气质量的空间非协同耦合规律:越靠近城市中心城区,空间协同耦合现象越显著,空间错位现象越弱;越远离主城区,空间非协同耦合现象越显著,空间错位现象越显著;SO2排放量与AOD在武汉市远城区的空间错位指数均大于0.7,且耦合度指数小于0.3,呈现较强的非协同耦合特征,NOX、VOCs、PM2.5的排放量与AOD在武汉中心城区的空间错位指数均小于0.5,且耦合度指数大于0.5,协同耦合现象较为显著。③ 基于时空非协同耦合分析城市大气环境污染治理建议:针对污染物与AOD空间错位不显著的城市中心城区,以本地减排治理为主;针对污染物与AOD空间错位显著的远城区,应在污染溯源分析的基础上进行区域协调综合治理。 相似文献
236.
Spatial associations between NDVI and environmental factors in the Heihe River Basin 总被引:1,自引:0,他引:1
Journal of Geographical Sciences - The Heihe River Basin is located in the arid and semi-arid regions of Northwest China. Here, the terrestrial ecosystem is vulnerable, making it necessary to... 相似文献
237.
Journal of Geographical Sciences - 相似文献
238.
Ci Song Ting Ma Yunyan Du Hua Shu Sihui Guo 《International journal of geographical information science》2019,33(1):134-154
An origin-destination (OD) flow can be defined as the movement of objects between two locations. These movements must be determined for a range of purposes, and strong interactions can be visually represented via clustering of OD flows. Identification of such clusters may be useful in urban planning, traffic planning and logistics management research. However, few methods can identify arbitrarily shaped flow clusters. Here, we present a spatial scan statistical approach based on ant colony optimization (ACO) for detecting arbitrarily shaped clusters of OD flows (AntScan_flow). In this study, an OD flow cluster is defined as a regional pair with significant log likelihood ratio (LLR), and the ACO is employed to detect the clusters with maximum LLRs in the search space. Simulation experiments based on AntScan_flow and SaTScan_flow show that AntScan_flow yields better performance based on accuracy but requires a large computational demand. Finally, a case study of the morning commuting flows of Beijing residents was conducted. The AntScan_flow results show that the regions associated with moderate- and long-distance commuting OD flow clusters are highly consistent with subway lines and highways in the city. Additionally, the regions of short-distance commuting OD flow clusters are more likely to exhibit ‘residential-area to work-area’ patterns. 相似文献
239.
The Ecological-living-productive land(ELPL) classification system was proposed in an effort to steer China's land pattern to an ecological-centered path, with the development model shifting from a single function into more integrated multifunction land use. The focus is coordinating the man-land contradictions and developing an intensive, efficient and sustainable land use policy in an increasingly tense relationship between humans and nature. Driven by socioeconomic change and rapid population growth, many cities are undergoing urban sprawl, which involves the consumption of cropland and ecological land and threatens the ecological balance. This paper aims to quantitatively analyze the critical effects of ELPL changes on eco-environmental quality according to land use classification based on leading function of ecology, living and production from 1990 to 2015 with a case study of Xining City. Also, four future land use scenarios were simulated for2030 using the Future Land Use Simulation(FLUS) model that couples human and natural effects. Our results show a decrease in productive land(PL) and an increase in ecological land(EL) and living land(LL) in Xining City. Forestry ecological land(FEL) covered the top largest proportion; agriculture productive land(APL) showed the greatest reduction and urban and rural living land(U-RLL) presented a dramatic increase. The eco-environmental quality improved in 1990-2010, mainly affected by the conversion of APL to FEL and GEL. However, the encroachment of U-RLL into APL, other ecological land(OEL) and FEL was the main contributor to the decline in eco-environmental quality in 2010-2015 as well as the primary reason for the increase area of lower-quality. The Harmonious Development(HD)-Scenario, characterized by a rational allocation of LL and PL and a better eco-environment, would have implications for planning and monitoring future management of ELPL, and may represent a valuable reference for local policy-makers. 相似文献
240.
琼东南盆地深水区松南-宝岛凹陷反转构造带发育特征及油气地质意义 总被引:1,自引:1,他引:0
利用新三维地震资料对松南-宝岛凹陷反转构造带发育特征、形成期次进行研究,并从构造背景及力学机制两个方面探讨反转构造的成因机制。研究结果表明,松南-宝岛凹陷反转构造带主要发育一系列"上凸下凹"的大型褶皱背斜,伴生NWW向弱走滑断裂构造和NNW向张剪构造。反转构造及其伴生构造符合NEE右旋剪切应力场特征,形成时间与东沙运动一致,表明该反转构造带可能受晚中新世南海东北部东沙运动产生的右旋走滑应力场作用控制。反转构造有利于研究区圈闭的重建和改造,对琼东南盆地东部新区油气运移和重新优选分配的认识,具有重要的油气地质意义。 相似文献