A biodiversity evaluation framework for restoration of aquatic macrophyte communities in shallow lakes driven by hydrological process management     

Shuhan Li  Tao Sun  Wei Yang  Baoshan Cui  Xinan Yin 《水文研究》2021,35(1):e13983

Macrophyte community diversity and composition respond to ecosystem conservation and local environmental factors. In this study, we developed a multidimensional diversity framework for macrophyte communities, including the taxonomic and functional alpha and beta diversity. We used the framework to explore the relationships among water level regimes and these diversity parameters in a case study of China's Baiyangdian Lake. Analysis of indicators of hydrologic alteration divided the water level from 1959 to 2019 into four regimes (dry, <6.42 m; low, 6.42–7.23 m; medium, 7.23–8.19 m; high, >8.19 m). Alpha and beta diversity were significantly higher in the medium regime than in the low and high regimes. Redundancy analysis indicated that the maximum water depth significantly affected taxonomic alpha diversity, and total nitrogen (TN) and chemical oxygen demand (COD) concentration significantly affected functional alpha diversity, respectively. Mantel tests showed that TN, Secchi depth (SD), and water depth in the high water level regime significantly increased the total beta diversity and turnover components. TN was the main factor that increased total taxonomic beta diversity. Water level regime mainly influenced interspecific relationships by changing the TN and COD concentration. The water level should be maintained between the medium and high water level regimes to promote restoration of the macrophyte community and improve ecosystem stability. The biodiversity evaluation framework would provide a deeper insight into the hydrological process management for restoration of aquatic macrophyte communities in shallow lakes.  相似文献   

An Early Cretaceous slab window beneath central Tibet,SW China: Evidence from OIB‐like alkaline gabbros in the Duolong area     

Hao Wu  Shulin Sun  Haiyong Liu  Hao Chu  Wei Ding 《地学学报》2019,31(1):67-75

The geodynamic mechanism of the late Early Cretaceous magmatic flare‐up in the collisional zone between the Lhasa and Qiangtang terranes in Tibet is controversial because of a scarcity of robust evidence. To address this problem, we report geochronological, geochemical and Hf isotopic data for the newly discovered Gufeng gabbros from the Duolong Cu–Au mineral district of the western Bangong–Nujiang Suture Zone (BNSZ). The gabbro samples, dated at 126.3 ± 1.8 Ma, show geochemical similarities to typical ocean island basalt (OIB) and have positive εHf(t) values of +3.3 to +6.9. The gabbros were generated by decompression melting of deep upwelling asthenosphere. This event is best explained by slab break‐off and the resultant development of a slab window beneath central Tibet.  相似文献   

Retrieving volume FeO and TiO_2 abundances of lunar regolith with CE-2 CELMS data using BPNN method     

Cai Liu  Hong-Yan Sun  Zhi-Guo Meng  Yong-Chun Zheng  Yu Lu  Zhan-Chuan Cai  Jin-Song Ping  Alexander Gusev  Shuo Hu 《天文和天体物理学研究(英文版)》2019,(5)

The volume FeO and TiO_2 abundances(FTAs) of lunar regolith can be more important for understanding the geological evolution of the Moon compared to the optical and gamma-ray results. In this paper, the volume FTAs are retrieved with microwave sounder(CELMS) data from the Chang'E-2 satellite using the back propagation neural network(BPNN) method. Firstly, a three-layered BPNN network with five-dimensional input is constructed by taking nonlinearity into account. Then, the brightness temperature(TB) and surface slope are set as the inputs and the volume FTAs are set as the outputs of the BPNN network.Thereafter, the BPNN network is trained with the corresponding parameters collected from Apollo, Luna,and Surveyor missions. Finally, the volume FTAs are retrieved with the trained BPNN network using the four-channel TBderived from the CELMS data and the surface slope estimated from Lunar Orbiter Laser Altimeter(LOLA) data. The rationality of the retrieved FTAs is verified by comparing with the Clementine UV-VIS results and Lunar Prospector(LP) GRS results. The retrieved volume FTAs enable us to re-evaluate the geological features of the lunar surface. Several important results are as follows. Firstly, very-low-Ti(1.5 wt.%) basalts are the most spatially abundant, and the surfaces with TiO_2 5 wt.% constitute less than 10% of the maria. Also, two linear relationships occur between the FeO abundance(FA) and the TiO_2 abundance before and after the threshold, 16 wt.% for FA. Secondly, a new perspective on mare volcanism is derived with the volume FTAs in several important mare basins, although this conclusion should be verified with more sources of data. Thirdly, FTAs in the lunar regolith change with depth to the uppermost surface,and the change is complex over the lunar surface. Finally, the distribution of volume FTAs hints that the highlands crust is probably homogeneous, at least in terms of the microwave thermophysical parameters.  相似文献   

短脉冲激光在实验室天体物理方面的研究进展     

孙嘉宁  袁大伟  王菲鹿 《天文研究与技术》2021,(2):248-254

随着啁啾脉冲放大技术(Chirped Pulse Amplification,CPA)的飞速发展,激光功率密度实现了飞跃式的提升,利用短脉冲激光开展实验室天体物理研究的条件日趋成熟。短脉冲激光与靶相互作用可以产生相对论粒子(正负电子、质子、中子等)和高能电磁辐射(X射线、γ射线),这些粒子和辐射的产生过程与天体中的某些物理现象相对应。介绍了利用短脉冲激光开展实验室天体物理的研究进展,重点介绍了核天体物理、空心离子光谱学、相对论无碰撞冲击波以及等离子体状态诊断等。  相似文献   

XTE J1550-564 2001年“迷你爆发”的X射线能谱研究          下载免费PDF全文

葛康  董爱军  刘畅  支启军 《天文学报》2021,62(4):35

黑洞X射线暂现源的迷你爆发是一类峰值光度较低、持续时间较短的爆发.由于观测数据较少,其物理机制仍不清楚.利用RXTE (Rossi X-ray Timing Explorer)卫星从2001年1月28日到3月14日的数据,研究了黑洞X射线暂现源XTE J1550–564 2001年迷你爆发的X射线能谱特性.发现在本次迷你爆发中, XTE J1550–564的X射线能谱可以用幂律谱很好地拟合.整个爆发的硬度强度图不是标准的q型,而是一直保持在最右侧.此外,还分析了此次爆发谱指数Γ与未吸收的2–10 keV能段的X射线流量F_(2–10 keV)的相关性,发现Γ-F_(2–10 keV)呈反相关关系,且谱指数Γ∈[1.35, 1.72].上述结果表明2001年这次爆发一直处于低/硬态,它的X射线辐射主要来自于辐射低效的吸积模式,如ADAF(Advection-Dominated Accretion Flow).  相似文献   

南极中山站全天信息采集系统     

王宇  辛玉新  姜鹏  杨勇  伦宝利  王传军  余晓光  常亮  范玉峰 《天文研究与技术》2021,(2):272-282

南极高原拥有独特的天文观测优势,为了对南极中山站夜天文观测条件进行实测研究,中国科学院云南天文台专门研制了一套具有耐低温、自动除雪除霜等适应南极气候特征的全自动全天信息采集系统,该系统可以提供实时的全天云量、天光背景和全天图像,并将信息推送到网页实时显示。介绍了系统的研制及为适应南极气候进行的耐低温实验,统计分析了中山站2016~2017年的全天信息数据,结果显示,中山站2016和2017年的可观测时间为772.21 h和437.38 h,可观测夜数为93 d和51 d,天光背景最大真实值为22.05 Mag/arcsec 2,年平均气温为-10.6℃,最高气温19.1℃,最低气温为-44℃,2016年平均相对湿度为55.2%。  相似文献   

Geophysical Signature of the Shallow Water Flow in the Deepwater Basin of the Northern South China Sea     

Xiaohua Zhang  Yunbao Sun  Shiguo Wu 《中国海洋大学学报(英文版)》2018,17(4):791-798

Shallow water flow (SWF), a disastrous geohazard in the continental margin, has threatened deepwater drilling operations. Under overpressure conditions, continual flow delivering unconsolidated sands upward in the shallow layer below the seafloor may cause large and long-lasting uncontrolled flows; these flows may lead to control problems and cause well damage and foundation failure. Eruptions from over-pressured sands may result in seafloor craters, mounds, and cracks. Detailed studies of 2D/3D seismic data from a slope basin of the South China Sea (SCS) indicated the potential presence of SWF. It is commonly characterized by lower elastic impedance, a higher Vp/Vs ratio, and a higher Poisson’s ratio than that for the surrounding sediments. Analysis of geological data indicated the SWF zone originated from a deepwater channel system with gas bearing over-pressured fluid flow and a high sedimentation rate. We proposed a fluid flow model for SWF that clearly identifies its stress and pressure changes. The rupture of previous SWF zones caused the fluid flow that occurred in the Baiyun Sag of the northern SCS.  相似文献   

Capsizing Probability of Dead Ship Stability in Beam Wind and Wave for Damaged Ship     

Hu  Li-fen  Zhang  Ke-zheng  Li  Xiao-ying  Chang  Run-xin 《中国海洋工程》2019,33(2):245-251

The International Maritime Organization has developed the second-generation intact stability criteria. Thus, damage stability criteria can be established in the future. In order to identity the capsizing probability of damaged ship under dead ship condition, this paper investigates two methods that can be used to research the capsizing probability in time domain, which mainly focus on the nonlinear righting lever GZ curve solution. One method subjects the influence of damaged tanks on the hull shape down to the wind and wave, and the other method is consistent with the real-time calculation of the GZ curve. On the basis of one degree of freedom rolling equation, the solution is Monte Carlo method, and a damaged fishery bureau vessel is taken as a sample ship. In addition, the results of the time-domain capsizing probability under different loading conditions are compared and analyzed. The relation of GM and heeling angle with the capsizing probability is investigated, and its possible reason is analyzed. On the basis of combining the time-domain flooding process with the capsizing probability calculation, this research aims to lay the foundation for the study of capsizing probability in time domain under dead ship condition, as well as provide technical support for capsizing mechanism of dead ship stability and damage stability criteria establishment in waves.  相似文献   

两株南极枝孢霉属真菌Cladosporium sp.NJF4和NJF6的次级代谢产物研究          下载免费PDF全文

常俊男  田晓清  樊成奇  黄金昌  陆亚男  韩清华 《极地研究》2020,32(1):60-67

南极因其独特的自然环境成为潜在、重要的微生物资源库,是产生新型生物活性物质和先导化合物菌株的潜在种源地,南极微生物正在成为创新药物研究新的重要资源。虽然近年来对南极微生物次级代谢产物的研究逐渐增加,但与温带和热带微生物研究相比仍处于初级阶段。对从南极普里兹湾海洋沉积物中获得的两株枝孢霉属真菌Cladosporium sp. NJF4和NJF6进行次级代谢产物分离及结构鉴定,获得20个化合物。化合物结构类型包括甾醇(1)、倍半萜类(7—8)、生物碱类(9—14)、二酮哌嗪(2—5、15—17)、芳香酸(6、18—19)等,其中倍半萜类(7—8)为首次从枝孢霉属真菌中分离得到,以上研究将为丰富南极微生物次级代谢产物库奠定一定的研究基础。  相似文献   

邮轮属性评价与品牌定位     

孙晓东  徐美华 《地理科学》2020,40(10):1688-1697

以全球最大的邮轮点评网站——邮轮评论家为数据来源渠道，以编辑（Editor/Expert）的文本点评以及对167艘邮轮10大属性的打分数据为样本，利用词频分析、回归分析、聚类分析和方差分析等方法，对全球21个邮轮品牌的产品属性、总体评价以及品牌定位问题进行了系统研究。结果表明，对于专业型游客来说，餐饮、客房和娱乐是关注度最高的船上属性，服务、性价比和公共空间是满意度最高的船上属性，客房、餐饮、公共空间、性价比和娱乐属性对邮轮总评具有显著影响。方差分析表明，与行业界定下的品牌行为相比，基于专业型游客感知的品牌划分更有效。  相似文献