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101.
Biogeochemical records of paleoenvironmental changes in Nainital Lake,Kumaun Himalayas,India 总被引:1,自引:0,他引:1
Preetam Choudhary Joyanto Routh Govind J. Chakrapani Bhishm Kumar 《Journal of Paleolimnology》2009,42(4):571-586
Rapid urbanization and increased tourism around Nainital Lake in the Kumaun Himalayan region in north India has raised concerns
about sediment and water pollution. Lead-210 dated sediment cores from the lake represent ~95 years of accumulation and yield
a mean sedimentation rate of ~4.7 mm year−1. Total organic carbon (TOC), percent N and S and their atomic C/N and C/S ratios, stable isotopes (δ13C, δ15N, and δ34S), and specific biomarkers (n-alkanes and pigments) were measured in the core. Organic matter is primarily derived from in-lake algal production and TOC
flux varies from 1.0 to 3.5 g m−2 year−1. Sediments are anoxic (Eh −328 to −187 mV) and have low (0.10–0.30 g m−2 year−1) N, but high (0.37–1.0 g m−2 year−1) S flux. Shifts in δ13C, δ15N, and δ34S suggest in-lake microbial processes dominated by denitrification and sulfate reduction. The sediments are dominated by short-chain
hydrocarbons with low Carbon Preference Index values. The pigments indicate a gradual shift to cyanobacterial domination of
the phytoplankton community in recent years. Despite an increase in external input of nutrients, the trophic state of the
lake has remained largely unchanged, and the perceived human-induced impacts are limited. 相似文献
102.
Stress Responses to Rapid Temperature Changes of the Juvenile Sea Cucumber (Apostichopusjaponicus Selenka) 总被引:2,自引:0,他引:2
DONG Yunwei JI Tingting DONG Shuanglin 《中国海洋大学学报(英文版)》2007,6(3):275-280
Activities of hexokinase (HK), pyruvate kinase (PK), superoxide dismutase (SOD) and catalase (CAT) and Hsp70 level were measured to evaluate the response of the commercially important sea cucumber (Apostichopus japonicus Selenka) to rapid temperature changes in laboratory. Animals were subjected to a higher temperature (from 10 to 20℃) (Tinc treatment) or to a lower temperature (from 20 to 10℃) (Tddec treatment) for 72 h. At 1, 3, 12, 24, 72 h of exposure, animals were removed and prepared for further analysis. Results showed that the effect of acute temperature changes on enzyme activities was significant. In Tinc treatment, activities of SOD and CAT increased immediately. The significant enhancement of SOD and CAT activities suggested that oxidative stress increases significantly when ambient temperature increasing from 10 to 20℃. The up-regulation of Flsp70 in Tinc and Tdec treatments indicated that Hsp70 was a bioindicator of thermal stress in the sea cucumber, and the expression pattern depended on the thermal treatment. 相似文献
103.
We present the second part of the results of our work to investigate the atmospheric parameters and chemical composition of
southern-hemisphere Cepheids obtained by analyzing 24 spectra for eight bright Cepheids and three semiregular bright supergiants
taken with the 1.9-m telescope of the South African Astronomical Observatory. The chemical composition and atmospheric parameters
have been determined for S Cru, AP Pup, AX Cir, S TrA, T Cru, R Mus, S Mus, U Car, V382 Car, HD 75276, and R Pup. 相似文献
104.
CCD photometry data of the T Tauri star H 187 are presented. They show that a new eclipse of this star began at the end of
2004. Since only one eclipse of this star has been observed previously with a duration of 3.5 years, our data indicate that
the eclipses of this object are periodic with a period P=4.9 years between eclipses. Thus, in terms of the absolute duration
of the eclipses and in terms of their relative length as a fraction of the period, H 187 is one of the most exotic objects
in the sky.
__________
Translated from Astrofizika, Vol. 48, No. 4, pp. 529–534 (November 2005). 相似文献
105.
Janice Brahney John J. Clague Brian Menounos Thomas W. D. Edwards 《Journal of Paleolimnology》2008,40(1):489-505
The level of Kluane Lake in southwest Yukon Territory, Canada, has fluctuated tens of metres during the late Holocene. Contributions
of sediment from different watersheds in the basin over the past 5,000 years were inferred from the elemental geochemistry
of Kluane Lake sediment cores. Elements associated with organic material and oxyhydroxides were used to reconstruct redox
fluctuations in the hypolimnion of the lake. The data reveal complex relationships between climate and river discharge during
the late Holocene. A period of influx of Duke River sediment coincides with a relatively warm climate around 1,300 years BP.
Discharge of Slims River into Kluane Lake occurred when Kaskawulsh Glacier advanced to the present drainage divide separating
flow to the Pacific Ocean via Kaskawulsh and Alsek rivers from flow to Bering Sea via tributaries of Yukon River. During periods
when neither Duke nor Slims river discharged into Kluane Lake, the level of the lake was low and stable thermal stratification
developed, with anoxic and eventually euxinic conditions in the hypolimnion. 相似文献
106.
基于主体功能区的京津冀城市群碳收支时空分异与碳补偿分区 总被引:2,自引:0,他引:2
从主体功能区划视角研究碳收支和碳补偿分区,对于制定适应各主体功能区低碳发展策略,推动区域生态环境协同治理,实现高质量发展具有重要意义,也是地理学思想对于实现“双碳”目标的重要贡献。本文首先构建主体功能区视角下碳收支与碳补偿的理论框架,然后以京津冀城市群157个县级单元为研究区,引入集中化指数、标准显性比较优势指数、SOM-K-means聚类等方法研究功能区视角下京津冀城市群碳收支时空分异与碳补偿分区,并提出以低碳发展为导向的碳减排空间优化方案。结果表明:① 2000—2017年京津冀城市群碳收支量呈现波动上升态势,其集中化指数均高于0.4的“警戒线”,碳收支地区差异整体偏大。② 碳收支时空分异显著,碳排放高值区呈现以京津唐为中心,向外逐步降低的“核心—外围”空间格局;而碳吸收空间格局趋于稳定,总体呈现东、北、西部高,而中、南部低的倒“U”型格局。③ 京津冀城市群碳收支与主体功能区战略定位较为吻合,优化开发区和重点开发区是碳排放的主要承压区,而重点生态功能区是碳吸收的优势主导区,各功能区碳吸收集中化指数差别较碳排放集中化指数小。④ 京津冀城市群共有53个支付区、64个平衡区和40个获补区,结合主体功能区规划战略目标,最终形成9类碳补偿空间优化区,并提出每一类型区低碳发展方向及策略。⑤ 未来要加强更微观尺度的碳收支及碳补偿研究,丰富和完善碳补偿理论框架,将碳补偿融入到碳交易市场,探索实现“双碳”目标的多元化路径。 相似文献
107.
?????????????????????????????????????????????μ?????????????????????????????????????????????????0.05 mm????????0.02 mm?????????????????????????????????÷??????? 相似文献
108.
WANGHai-xia WANZhong-juan YUShao-peng LUOXin-zheng SUNGuang-you 《中国地理科学(英文版)》2004,14(2):179-185
Although the Songnen Plain in the northeastern China was developed relatively late in the temperate zone of the world, its eco-environment has changed greatly. This paper analyzes the changes of land cover and the rates and trends ofdesertification during the past 100 years in the Songnen Plain. According to the macroscopic analysis, we find that the eco-environment in the plain has reached to the threshold of catastrophic change since the 1950s. The Thorn Needle Catastrophic Model was used to determine and validate this conclusion. Human activities, including large-scale construction projects, such as huge dams and dikes, and excessive grazing were the primary factors contributing to regional eco-environmental catastrophe. And irrational reclamation of the wilderness also affected the eco-environmental change. The results reveal the complex human-land interactions. 相似文献
109.
Marco Bassetto Lorenzo Niccolai Alessandro A. Quarta Giovanni Mengali 《Celestial Mechanics and Dynamical Astronomy》2018,130(2):18
Analytic solutions to continuous thrust-propelled trajectories are available in a few cases only. An interesting case is offered by the logarithmic spiral, that is, a trajectory characterized by a constant flight path angle and a fixed thrust vector direction in an orbital reference frame. The logarithmic spiral is important from a practical point of view, because it may be passively maintained by a Solar sail-based spacecraft. The aim of this paper is to provide a systematic study concerning the possibility of inserting a Solar sail-based spacecraft into a heliocentric logarithmic spiral trajectory without using any impulsive maneuver. The required conditions to be met by the sail in terms of attitude angle, propulsive performance, parking orbit characteristics, and initial position are thoroughly investigated. The closed-form variations of the osculating orbital parameters are analyzed, and the obtained analytical results are used for investigating the phasing maneuver of a Solar sail along an elliptic heliocentric orbit. In this mission scenario, the phasing orbit is composed of two symmetric logarithmic spiral trajectories connected with a coasting arc. 相似文献
110.
众多研究人员在网络GIS的研究方面都习惯将其内容简单化为WebGIS或者Internet/Intranet GIS。实际上,WebGIS和Internet/Intranet GIS在数据模型、网络架构、体系构建和功能部署等方面都有较大的区别,这种将We-bGIS和Internet/Intranet GIS统称为网络GIS的做法本身就有缺陷。本文以网络和分布式计算技术为基础,从“广义”和“狭义”的角度对网络GIS的概念框架、内容体系和应用等几个方面做了重构研究,以期推动网络GIS的研究进展。 相似文献