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Frequency Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
It seems almost certain that optical atomic standards will have a huge impact on the future of frequency metrology. Optical standards operate at much higher resonance frequencies than microwave standards; the stabilized lasers that serve as their resonators typically operate at a frequency near 1015 Hz, as opposed to less than 1010 Hz for cesium. As a result, these standards promise accuracies and stabilities that are several orders of magnitude better than the best microwave standards. Optical frequency standards have been constructed at NIST utilizing single-ion techniques based on mercury (199Hg+) and aluminum (27Al+), as well as neutral atom techniques based on calcium (40Ca), ytterbium (174Yb), and strontium (87Sr). It appears likely that the SI second will eventually be redefined, with the new definition based on one of these optical atomic transitions [20].
Evolution of diagenetic fluids in the deeply buried, upper Ediacaran Dengying Formation, Central Sichuan Basin, China
Published in Australian Journal of Earth Sciences, 2023
Y. J. Hu, C. F. Cai, Y. Li, R. Zhou, Y. J. Tang, J. F. Hu, F. C. Lu, P. Sun
The deeply buried upper Ediacaran Dengying Formation (ca 551.1–541 Ma; Condon et al., 2005) in the Sichuan Basin hosts a giant gas reserve. This formation, together with the overlying Cambrian sequence, is reported to have 1 trillion cubic metres of gas (Zou et al., 2014). Bulk analyses of major, trace and rare earth elemental contents, carbon (δ13C), oxygen (δ18O) and strontium (87Sr/86Sr) isotopic compositions of host facies and diagenetic carbonate have been performed to decipher the evolution from depositional settings to deep-burial regimes (Feng et al., 2017; Hu, Cai, Liu, et al., 2020; Hu, Cai, Pederson, et al., 2020; Zhu et al., 2020). However, the occurrence of many types of lithologies and diagenetic minerals requires detailed petrographic observations and high-resolution geochemical analyses (Peng et al., 2018). For example, in situ rare earth elemental data on fibrous dolomite cement show a seawater-like pattern compared with bulk-rock results (Hu, Cai, Liu, et al., 2020). Moreover, the reservoir performance of limestone is poorly understood.