科研成果 by Type: 期刊论文

The classical gradient-diffusion hypothesis has known deficiencies when applied to cooling applications. In this paper, the gene-expression programming (GEP) method, a machine learning approach, has been applied to develop scalar-flux models via symbolic regression. The scalar-flux, the unclosed term of the mean passive-scalar transport equation, is treated by considering the polynomial basis and scalar invariants available from computable Reynolds-averaged quantities. This method has been applied to develop and then assess a model for the test case of jet in crossflow. A high-fidelity database was first probed for insight into which of the candidate bases are the most suitable as modelling terms. The high dimensionality of the function space, spanned by the basis, was then reduced by basic statistical techniques. The resulting data-driven model is presented and tested for a range of different jet in crossflow cases. Compared with eddy-diffusivity models, the new model is shown to produce reliably more accurate results. This demonstrates that the current framework can be used for scalar-flux modelling in complex three-dimensional flows and has potential to provide generalized form closures with improved predictive accuracy for the same classes of flows they were trained on.

Increased human water use combined with climate change have aggravated water scarcity from the regional to global scales. However, the lack of spatially detailed datasets limits our understanding of the historical water use trend and its key drivers. Here, we present a survey-based reconstruction of China’s sectoral water use in 341 prefectures during 1965 to 2013. The data indicate that water use has doubled during the entire study period, yet with a widespread slowdown of the growth rates from 10.66 km3·y−2 before 1975 to 6.23 km3·y−2 in 1975 to 1992, and further down to 3.59 km3·y−2 afterward. These decelerations were attributed to reduced water use intensities of irrigation and industry, which partly offset the increase driven by pronounced socioeconomic development (i.e., economic growth, population growth, and structural transitions) by 55% in 1975 to 1992 and 83% after 1992. Adoptions for highly efficient irrigation and industrial water recycling technologies explained most of the observed reduction of water use intensities across China. These findings challenge conventional views about an acceleration in water use in China and highlight the opposing roles of different drivers for water use projections.

Based on the concepts of “ancient China studies” and “digital humanities” (DH) in the context of China, this paper first gives a brief review on the development and practice of DH cyberinfrastructure. Under a series of reflections and a brief investigation on ancient Chinese literatures and traditional humanistic activities, this paper puts forward a new DH cyberinfrastructure conceptual model for ancient China studies that can bring people, information, and computational tools together and allow humanistic scholars to perform in a new way and with higher efficiency. On the premise of actual practices to turn a conceptual model into reality, this paper discusses DH cyberinfrastructure and the future of academic libraries.

Abstract The mechanism of aggregation-induced emission, which overcomes the common aggregation-caused quenching problem in organic optoelectronics, is revealed by monitoring the real time structural evolution and dynamics of electronic excited state with frequency and polarization resolved ultrafast UV/IR spectroscopy and theoretical calculations. The formation of Woodward?Hoffmann cyclic intermediates upon ultraviolet excitation is observed in dilute solutions of tetraphenylethylene and its derivatives but not in their respective solid. The ultrafast cyclization provides an efficient nonradiative relaxation pathway through crossing a conical intersection. Without such a reaction mechanism, the electronic excitation is preserved in the molecular solids and the molecule fluoresces efficiently, aided by the very slow intermolecular charge and energy transfers due to the well separated molecular packing arrangement. The mechanisms can be general for tuning the properties of chromophores in different phases for various important applications.

Over the past few decades, anaerobic ammonium oxidation (anammox) has been extensively documented at different scales in natural ecosystems. Previous studies have stated that the community composition of anammox bacteria is shaped mainly by environmental factors, whereas spatial factors have been largely overlooked. This study investigated biogeographical patterns of anammox bacterial communities using 42 sediment samples along a 4300-km stretch of the Yangtze River, the longest river in Asia. A significant distance-decay relationship was observed for anammox bacterial community similarity, which was significantly influenced by mean dendritic distance rather than environmental factors. This implied that dispersal limitation plays an important role in shaping biogeographical pattern of anammox community. Furthermore, our results revealed that neutral processes played vital role in shaping community assembly of anammox bacteria, and their communities were seriously dispersal limited. These findings contrast with previous studies on community similarities between broad taxonomic groups, which are mainly determined by niche-based selection owing to greater niche distances within broad taxonomic groups than in anammox bacteria. Importantly, the slope of the distance-decay curve was much steeper than previously reported for whole bacteria, which indicating the species turnover rate of anammox bacterial community was significantly higher than that of the whole bacterial community. Anammox bacteria harbor strong adhesion ability and low dispersal potential, and ultimately exhibited a high species turnover rate. Together, in the context of biogeography, our results highlight the importance of dispersal limitation in shaping the biogeographical pattern of anammox bacterial community.