Geological and paleomagnetic data indicate that the ice sheets might have extended to low-latitude regions in the Cryogenian (720-635 Ma). The 'snowball Earth' hypothesis proposed that the Earth was completely icecovered during global glaciation. However, the glacial sedimentary record seems to contradict with the snowball Earth hypothesis. Detailed sedimentological investigations of the glacial deposits would provide the first-order constraint on the nature of global glaciation. The Nantuo Formation (∼654-635 Ma) in the Yangtze Block of South China has been correlated with the Marinoan snowball Earth. In this study, we conducted systematic sedimentological analyses of six sections/cores of the Nantuo Formation. Three facies associations were recognized: the proximal glaciomarine, distal glaciomarine, and non-glacial marine facies associations. The vertical stacking pattern of facies associations can be correlated among the five slope and basin sections, while their correlation with the shelf section remains obscure. Our data indicate two episodes of glaciation that are separated by an interglacial interval during the Nantuo Glaciation. The first glacial episode is recorded by successions of coarse-grained facies (e.g., massive diamictite) in the lower part of the Nantuo Formation. The re-appearance of massive diamictite in the middle to upper part of the Nantuo Formation indicates onset of the second glacial episode. These two glacial episodes were separated by a siltstone/shale sequence of several 10 s m thick, suggesting an interglacial period with limited influence from glaciation. The top of Nantuo Formation consists of alternative distal-glaciomarine and non-glacial marine facies associations, representing the deglacial sequence of the Nantuo Glaciation. The sedimentary facies analysis indicates that the cold climate during the Nantuo Glaciation may be cyclic. Finally, our sedimentary analysis confirms a lag between the deglaciation and precipitation of cap carbonate.
Ternary optical computer(TOC) has become a research hotspot in the field because of the advantages such as inherent parallelism, numerous trits, low power consumption, extendibility, bitwise allocability and dynamical bitwise reconfigurability. Meanwhile, its performance evaluation attracts more and more attentions from potential users and researchers. To model its computing ecology more accurately, this paper first builds a three-staged TOC service model by introducing asynchronous multi-vacations and tandem queueing, and then proposes a task scheduling algorithm and an optical processor allocation algorithm with asynchronous vacations of some small optical processors after dividing equally the entire optical processor into several small optical processors which can be used independently. At the same time, the analytical model was established to obtain important performance indicators such as response time, the number of tasks and utilization of optical processor, based on M/M/1 and M/M/n queuing system with asynchronous multi-vacations. In addition, relevant numerical simulation experiments are conducted. The results illustrate that the number of small optical processors, vacation rate and the number of small optical processors allowed to be on vacation have important effects on the system performance. Compared with synchronous vacation, asynchronous vacation not only ensures the system to obtain better maintenance but also improves the system performance to some degree.
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