| 1. |
- Dong, Haoxuan, et al.
(author)
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Flexible Eco-cruising Strategy for Connected and Automated Vehicles with Efficient Driving Lane Planning and Speed Optimization
- 2024
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In: IEEE Transactions on Transportation Electrification. - 2332-7782. ; 10:1, s. 1530-1540
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Journal article (peer-reviewed)abstract
- Eco-cruising control of vehicles is a potential approach for improving vehicle energy efficiency and reducing travel time. However, many eco-cruising studies merely focused on vehicle longitudinal speed optimization but overlooked the lane change maneuvers, which may impair the benefits of eco-cruising when the vehicle encounters the slowly moving preceding vehicle. This study proposes a flexible eco-cruising strategy (FECS) with efficient driving lane planning and speed optimization capabilities simultaneously for connected and automated vehicles. The FECS is designed with a hierarchical control framework, where the first layer uses the Dijkstra algorithm to plan an efficient driving lane sequence considering the long-term effect of the preceding vehicles, then guides the second layer to optimize the vehicle’s speed for saving energy using trigonometric speed profile. The optimized driving trajectory is implemented in the third layer by regulating the speed and yaw angle for guaranteeing safe inter-vehicle distance when uncertainties are present. Finally, stochastic simulation with randomized traffic flows and typical case analysis based on real-world traffic data are conducted to demonstrate the performance of the FECS. The results manifest FECS’s capability of lowering driving costs in moderate-flow and free-flow traffic. However, we note that the benefits are less pronounced in congested-flow traffic.
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| 2. |
- Li, Xinxi, et al.
(author)
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Increasing importance of precipitation in spring phenology with decreasing latitudes in subtropical forest area in China
- 2021
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In: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923. ; 304-305
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Journal article (peer-reviewed)abstract
- Climate warming has significantly advanced plant spring phenology in temperate and boreal biomes in the northern hemisphere. However, the response of subtropical forest phenology to climate change remains largely unclear. This study aimed to determine the spatiotemporal patterns of spring photosynthetic phenology in subtropical forests in China over the period 2002-2017 and explore its underlying mechanism in response to the changes of different climate variables. We applied four methods to extract the start of the photosynthetic period (SOP) from a solar–induced chlorophyll fluorescence (SIF) data set during the period 2002 to 2017, and determined correlations between SOP and environmental factors using partial correlation analyses. Overall, the SOP was advanced by 6.8 days. Furthermore, we found that the SIF-based SOP is highly correlated with the flux data–based photosynthetic onset dates, demonstrating that SIF can be a useful index in characterizing the photosynthetic phenology in subtropical forests. Interestingly, based on partial correlation analysation temperature dominated the SOP in the northern subtropical forest, but the importance of precipitation increased with decreasing latitudes, and the primary climatic control of SOP in southern monsoon evergreen forests is precipitation. These results suggested that the predicted increase in temperature and shift in precipitation regimes under ongoing climate change might potentially largely affect the photosynthetic phenology, and thus affect the carbon and water cycles in subtropical forests.
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| 3. |
- Piao, Shilong, et al.
(author)
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Evidence for a weakening relationship between interannual temperature variability and northern vegetation activity.
- 2014
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5
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Journal article (peer-reviewed)abstract
- Satellite-derived Normalized Difference Vegetation Index (NDVI), a proxy of vegetation productivity, is known to be correlated with temperature in northern ecosystems. This relationship, however, may change over time following alternations in other environmental factors. Here we show that above 30°N, the strength of the relationship between the interannual variability of growing season NDVI and temperature (partial correlation coefficient RNDVI-GT) declined substantially between 1982 and 2011. This decrease in RNDVI-GT is mainly observed in temperate and arctic ecosystems, and is also partly reproduced by process-based ecosystem model results. In the temperate ecosystem, the decrease in RNDVI-GT coincides with an increase in drought. In the arctic ecosystem, it may be related to a nonlinear response of photosynthesis to temperature, increase of hot extreme days and shrub expansion over grass-dominated tundra. Our results caution the use of results from interannual time scales to constrain the decadal response of plants to ongoing warming.
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