Irrigation modernization impacts irrigation energy consumption and greenhouse gas (GHG) emissions, enhancing irrigation water efficiency. To systematically examine the impact of irrigation system modernization on China's irrigation energy consumption and GHG emissions, a scenario-decomposition-based calculation method of irrigation energy consumption and GHG emissions at national and provincial scales based on the physical processes of irrigation energy consumption was proposed. The relationship between irrigation water consumption, energy consumption, and GHG emissions during the rapid development period (2005–2015) of water-saving irrigation technology in China was clarified. The data demonstrate that the irrigation water volume and energy consumption increased by 7.9% and 22.3%, respectively, from 2005 to 2015, and the national equivalent of GHG reached 42.5 Mt CO2e in 2015. Water-energy consumption across the country was extremely divergent. The irrigation energy consumption per unit volume of water and per unit area is 3.74 and 2.88 times more in the northern provinces than in the southern provinces. Promoting water-saving irrigation technology can effectively improve China's irrigation water-energy-GHG emissions structure, which can help improve irrigation efficiency while ensuring no dramatic increase in irrigation energy consumption. Water-saving irrigation technologies should be promoted following the local conditions throughout the country. The relationship between irrigation water-energy-GHG emissions in northern provinces should be considered significantly.
Monolayer 2D semiconductors provide an attractive option for valleytronics due to the valley-addressability by helicity-specific light beam. But the short valley lifetime for excitons have hindered potential valleytronic applications. In this paper, we demonstrate a strategy for prolonging the valley lifetime by converting excitons to trions through effective gate control and by taking advantage of much longer valley lifetime for trions than for excitons. In continuous-wave experiments, we found the valley polarization increases as gate voltage is tuned away from the charge neutrality, with the degree of valley polarization increased from near zero to 38 % for excitons and to 33 % for trions. This is the first successful observation of valley-polarization in MoTe2 without a magnetic field. In pump-probe experiments, we found that the intervalley scattering process of excitons is significantly suppressed as gate voltage is tuned away from charge neutrality, with scattering time from 0.85 ps to ~ 2.17 ps. In contrast, the intervalley scattering rate for trions increases due to increased availability of partner charges for trion spin flipping, with scattering time from 1.39 ns down to ~100 ps away from charge neutrality. Interestingly, our results show that, despite the accelerated intervalley scattering, the trion polarization degree increases due to polarized trion generation from the exciton-to-trion conversion overtaking the intervalley trion scatterings. Importantly, the efficient exciton-to-trion conversion changed the dominant depolarization mechanisms. As a result, the valley lifetime is dramatically improved by 1000 times from excitons to trions at the charge neutrality. Our results shed new light into the depolarization dynamics and the interplay of various depolarization channels for excitons and trions and provide an effective strategy for prolonging the valley polarization.
Two-dimensional (2D) semiconductors have emerged as promising candidates for various optoelectronic devices especially electroluminescent (EL) devices. However, progress has been hampered by many challenges including metal contacts and injection, transport, and confinement of carriers due to small sizes of materials and the lack of proper double heterostructures. Here, we propose and demonstrate an alternative approach to conventional current injection devices. We take advantage of large exciton binding energies in 2D materials using impact generation of excitons through an alternating electric field, without requiring metal contacts to 2D materials. The conversion efficiency, defined as the ratio of the emitted photons to the preexisting carriers, can reach 16% at room temperature. In addition, we demonstrate the first multiwavelength 2D EL device, simultaneously operating at three wavelengths from red to near-infrared. Our approach provides an alternative to conventional current-based devices and could unleash the great potential of 2D materials for EL devices.
China’s kiwi industry has seen rising production costs and shrinking planting areas in recent years; at the same time, the lack of professional production standards leads to the input redundancy and waste of production factors in the production process of kiwifruit, which intensifies the dilemma of unsustainable agricultural production. This has brought more and more serious challenges to the sustainable development of the industry. In order to solve this problem and clarify the composition and utilization efficiency of energy in the production process of kiwifruit, this study took Chinese kiwifruit production as the research object and analyzed the energy input and output under surface irrigation and water-saving irrigation from the perspective of energy. The results show that the energy input of kiwifruit production under traditional surface irrigation was 85.4 GJ/ha, and the energy output was 59.7 GJ/ha. Among all energy input elements, mineral fertilizers accounted for the highest proportion of energy input, accounting for 48.31%. Under water-saving irrigation, the energy input and output of kiwifruit production are 72.3 GJ/ha and 62.3 GJ/ha; the highest energy input is also mineral fertilizer. The data envelopment analysis results also confirmed that there is a large redundancy in the amount of mineral fertilizer. Compared with surface irrigation, water-saving irrigation technology has effectively improved the energy ratio (from 0.70 to 0.86), energy productivity (from 0.37 kg/MJ to 0.45 kg/MJ) as well as net energy (from −25.8 GJ/ha to −9.93 GJ/ha). Thus, promoting the application of water-saving irrigation technology and increasing the proportion of fertigation during the kiwi production process are necessary measures to promote the sustainable development of China’s kiwi industry.
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