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121.
为科学评价测量结果的可靠性,对海水中137Cs γ能谱分析方法的不确定度进行了评估。根据《化学分析中不确定度的评估指南》,分析不确定度的来源并逐一对各不确定度分量进行了量化,最终计算了合成相对标准不确定度。结果表明,影响海水中137Cs γ能谱测量不确定度的因素分别为样品源137Cs峰区计数、标准源活度、取样体积、化学回收率、本底137Cs峰区计数及标准源137Cs峰区计数,其中样品源137Cs峰区计数的不确定度贡献最为突出。对于137Cs活度浓度为1.28 mBq/L的海水样品,其合成相对标准不确定度为9.78%。 相似文献
122.
Aharon Oren Deng Tianlong Shadrin Nikolai V. Zheng Mianping Zadereev Egor S. 《中国海洋湖沼学报》2018,36(6):1901-1906
正Thestatementthattheworld’secosystemsare rapidly deteriorating due to human intervention and global warming is nowadays commonplace. Some o the ecosystems most heavily impacted are inland sal lakes. The salt lakes are among the most valuable and fascinating ecosystems on Earth, and their study has both basic scientifi c interest as well as applied aspects 相似文献
123.
Deepwater sediments are prone to loss circulation in drilling due to a low overburden gradient. How to predict the magnitude of leak-off pressure more accurately is an important issue in the protection of drilling safety and the reduction of drilling cost in deep water. Starting from the mechanical properties of a shallow formation and based on the basic theory of rock-soil mechanics, the stress distribution around a borehole was analyzed. It was found that the rock or soil on a borehole is in the plastic yield state before the effective tensile stress is generated, and the effective tangential and vertical stresses increase as the drilling fluid density increases; thus, tensile failure will not occur on the borehole wall. Based on the results of stress calculation, two mechanisms and leak-off pressure prediction models for shallow sediments in deepwater drilling were put forward, and the calculated values of these models were compared with the measured value of shallow leak-off pressure in actual drilling. The results show that the MHPS (minimum horizontal principle stress) model and the FIF (fracturing in formation) model can predict the lower and upper limits of leak-off pressure. The PLC (permeable lost circulation) model can comprehensively analyze the factors influencing permeable leakage and provide a theoretical basis for leak-off prevention and plugging in deepwater drilling. 相似文献
124.
Yan Zheng-zhou Lu Xiao-meng Tian Jian-feng Zhang Chun-guang Wang Kun Deng Li-cai 《Chinese Astronomy and Astrophysics》2018,42(4):609-625
Driven by the technological advancements and scientific objectives, the data acquisition in observational astronomy has been changed greatly in recent years. Fully automated or even autonomous ground-based network of telescopes has now become a tendency for time-domain observational projects. The Stellar Observations Network Group (SONG) is an international collaboration with the participation and contribution of the Chinese astronomy community. The scientific goal of SONG is time-domain astrophysics, such as the astroseismology and the research of variable stars in open clusters. The SONG project aims to build a global network of one-meter telescopes equipped with high-precision and high-resolution spectrographs, and two-channel lucky-imaging cameras. It is the Chinese initiative to install a 50 cm binocular photometry telescope at each SONG node to share the network platform and infrastructure. This work is focused on the design and implementation of SONG/50BiN in technology and methodology, for the ground-based network composed of multiple sites and a variety of instruments. 相似文献
125.
126.
利用百分位阈值方法定义极端事件,从极端事件再现时间的角度,研究了极端事件发生时间间隔的长程相关性.发现若原时间序列具有长程相关性,则它的极端事件再现时间序列也具有长程相关性;计算表明两者的标度指数α相当接近,这一特性与随机产生的再现时间序列有着本质的差别,再现时间序列的长程相关性是由原序列的长程相关性决定的.具有长程相关性的时间序列再现时间的概率分布明显不同于随机序列,其小值再现时间的概率较大,反映出极端事件的群发现象.本文根据这一特征定义了再现时间的群发性指数,发现时间序列的长程相关性是导 相似文献
127.
We describe the microfabrication of 85Rb vapour cells using a glass-silicon anodic bonding technique and in situ chemical reaction between rubidium chloride and barium azide to produce Rb. Under controlled conditions, the pure metallic Rb drops and buffer gases were obtained in the cells with a few mm3 internal volumes during the cell sealing process. At an ambient temperature of 90 ℃ the optical absorption resonance of 85Rb D1 transition with proper broadening and the corresponding coherent population trapping (CPT) resonance, with a signal contrast of 1.5% and linewidth of about 1.7 kHz, have been detected. The sealing quality and the stability of the cells have also been demonstrated experimentally by using the helium leaking detection and the after-9-month optoelectronics measurement which shows a similar CPT signal as its original status. In addition, the physics package of chip-scale atomic clock (CSAC) based on the cell was realized. The measured frequency stability of the physics package can reach to 2.1×10-10 at one second when the cell was heated to 100 ℃ which proved that the cell has the quality to be used in portable and battery-operated devices. 相似文献
128.
The electronic structures and effective masses of the N mono-doped and Al-N, Ga-N, In-N codoped ZnO system have been calculated by a first-principle method, and comparisons among different doping cases are made. According to the results, the impurity states in the codoping cases are more delocalised compared to the N mono-doping case, which means a better conductive behaviour can be obtained by codoping. Besides, compared to the Al-N and Ga-N codoping cases, the hole effective mass of In-N codoped system is much smaller, indicating the p-type conductivity can be more enhanced by In-N codoping. 相似文献
129.
We conducted studies of phytoplankton and hydrological variables in a semi-enclosed bay in northern China to understand the spatial–temporal variability and relationship between these variables. Samples were collected during seven cruises in Jiaozhou Bay from November 2003 to October 2004, and were analyzed for temperature, nutrients and phytoplankton pigments. Pigments from eight possible phytoplankton classes (Diatoms, Dinoflagellates, Chlorophyceae, Prasinophyceae, Chrysophyceae, Haptophyceae, Cryptophyceae and Caynophyceae) were detected in surface water by high performance liquid chromatography (HPLC). Phytoplankton pigment and nutrient concentrations in Jiaozhou Bay were spatially and temporally variable, and most of them were highest in the northern and eastern parts of the sampling regions in spring (May) and summer (August), close to areas of shellfish culturing, river estuaries, dense population and high industrialization, reflecting human activities. Chlorophyll a was recorded in all samples, with an annual mean concentration of 1.892 μg L−1, and fucoxanthin was the most abundant accessory pigment, with a mean concentration of 0.791 μg L−1. The highest concentrations of chlorophyll a (15.299 μg L−1) and fucoxanthin (9.417 μg L−1) were observed in May 2004 at the station close to the Qingdao Xiaogang Ferry, indicating a spring bloom of Diatoms in this area. Although chlorophyll a and other biomarker pigments showed significant correlations, none of them showed strong correlations with temperature and nutrients, suggesting an apparent de-coupling between the pigments and these hydrological variables. The nutrient composition and phytoplankton community composition of Jiaozhou Bay have changed significantly in the past several decades, reflecting the increasing nutrient concentrations and decline of phytoplankton cell abundance. The unchanged total chlorophyll a levels indicated that smaller species have filled the niche vacated by the larger species in Jiaozhou Bay, as revealed by our biomarker pigment analysis. 相似文献
130.