Subjects: Physics >> Nuclear Physics submitted time 2023-09-04 Cooperative journals: 《核技术》
Abstract： Backgroundβ-decay half-life is one of the fundamental physical properties of unstable nuclei and plays an important role in nuclear physics and astrophysics. PurposeThis study aimed to provide accurate nuclear β-decay half-life predictions and reasonable uncertainties associated with the predictions. MethodsNuclear β-decay half-lives were studied based on the Bayesian neural network (BNN) approach. Three types of neural networks with x = (Z, N), x = (Z, N, Qβ), and x = (Z, N, δ, Qβ) were constructed as inputs to explore the influence of the input on the prediction. The posterior distributions were sampled using the Markov chain Monte Carlo algorithm. The mathematical expectations and standard deviations of the neural network predictions on the posterior distributions were used as the predicted values and errors of the BNN approach. ResultsThe learning accuracy can be significantly improved by incorporating the β-decay energy and physical quantity related to the nuclear pair effect into the neural network input layer and then using the logarithm of β-decay half-life as the network output. For nuclei with half-lives of less than 1 s, the prediction accuracy is approximately 0.2 orders of magnitude, which is similar to that afforded by the BNN method by learning the differences between the logarithms of the experimental half-lives and theoretical results. ConclusionsThe Bayesian neural network can accurately predict β-decay half-lives. When extrapolated to the unknown nuclear region, the predicted β-decay half-lives agree with the results of other theoretical models within errors, especially for nuclei with Z ≳ 50.
Subjects: Other Disciplines >> Synthetic discipline submitted time 2023-03-28 Cooperative journals: 《中国科学院院刊》
Abstract： Beijing-Tianjin-Hebei region, Yangtze River Delta, and Guangdong-Hong Kong-Macao Greater Bay Area are the three largest urban agglomerations in China, and have been increasingly becoming the core engines of China’s economic growth. Nevertheless, rapid regional urbanization accompanying high-intensity human activities has also brought enormous social and environmental pressure in these urban agglomerations, posing a grand challenge to urban and regional sustainability. This study conducts a cross-urban agglomeration comparison of the ecological and environmental changes over the past two decades. Using a combination of remotely sensed data, in-situ monitoring data, and environmental statistic data, the changes in four dimensions are quantified, namely ecological quality, environmental quality, resource and energy use efficiency, and eco-environmental governance capacity. Further, the effectiveness of environmental policies and initiatives is evaluated at the national and urban agglomeration levels. It is found that the quality of ecological land has increased steadily since 2000, with increased provision of ecosystem services. Air quality and water quality have been substantially improved, and the use of resources and energy efficiency have been greatly improved. The pollution emissions per unit GDP have been greatly reduced. The ecological and environmental infrastructures have become increasingly available, along with gradually strengthened governance capacity on environmental protection and ecological restoration. The National 10th to 13th Five-Year Plan for Environmental Protection played a significant role in environmental protection and ecological restoration across mega urban agglomerations. The environmental challenges, of urban agglomerations faced now and in the future, are also discussed, so as to the policies and actions that need to be addressed.
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