| 11. |
- Liu, Siyu, et al.
(författare)
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Experimental exploration of potassium compounds in the vicinity of a burning biomass pellet : From near-surface to downstream
- 2024
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Ingår i: Proceedings of the Combustion Institute. - 1540-7489. ; 40:1-4
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Tidskriftsartikel (refereegranskat)abstract
- The concentrations of gas-phase potassium hydroxide (KOH), potassium chloride (KCl) and atomic potassium (K(g)) were quantitatively measured from the near-surface to downstream area of burning pinewood pellets by a newly developed photofragmentation tunable diode laser absorption spectroscopy (PF-TDLAS) technique to reveal the original form of the released potassium. The novel arrangement of the PF-TDLAS system enabled a spatial resolution of ∼1 mm3, which made it possible to obtain temporal release profiles of K(g)/KOH/KCl at different heights above the burning pellet surface. Surface temperature and mass loss of the wood pellet as well as the gas temperature at measurement points were measured simultaneously. During the devolatilization stage, the release of all three potassium species was observed, with each of them accounting for ∼1/3; while in char oxidation stage, the release of KOH was dominant, but the release intensity was strongly influenced by the local oxygen content. The results from different measurement heights showed there was a notable difference in potassium release profiles of different potassium species over the near-surface area, where the detected potassium forms were the best representative of the originally released forms of potassium. For a period of time during the devolatilization stage, only K(g) was detected in the near-surface area, and the concentration was significantly lower than the downstream area where KOH and KCl coexisted. This suggested that a large amount of potassium might leave the pellet as organic-K, which cannot be detected by the PF-TDLAS method. During char oxidation stage, the total potassium concentration at the near-surface area was also lower than the downstream area, but it was due to the lack of oxygen at the measurement position. A potassium release mechanism during the devolatilization stage of biomass combustion was proposed based on the experimental measurements, and the results also indicated the importance of spatially resolved measurement.
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| 12. |
- Villaescusa-Navarro, Francisco, et al.
(författare)
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The Quijote Simulations
- 2020
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 250:1
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Tidskriftsartikel (refereegranskat)abstract
- The QUIJOTE simulations are a set of 44,100 full N-body simulations spanning more than 7000 cosmological models in the {Omega(m), Omega(b), h, n(s), sigma(8), M-nu, w} hyperplane. At a single redshift, the simulations contain more than 8.5 trillion particles over a combined volume of 44,100 (h(-1) Gpc)(3); each simulation follows the evolution of 256(3), 512(3), or 1024(3) particles in a box of 1 h(-1) Gpc length. Billions of dark matter halos and cosmic voids have been identified in the simulations, whose runs required more than 35 million core hours. The QUIJOTE simulations have been designed for two main purposes: (1) to quantify the information content on cosmological observables and (2) to provide enough data to train machine-learning algorithms. In this paper, we describe the simulations and show a few of their applications. We also release the petabyte of data generated, comprising hundreds of thousands of simulation snapshots at multiple redshifts; halo and void catalogs; and millions of summary statistics, such as power spectra, bispectra, correlation functions, marked power spectra, and estimated probability density functions.
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| 13. |
- Wang, Chunyu, et al.
(författare)
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Co-regulation of temperature and moisture in the irrigated agricultural ecosystem productivity
- 2023
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Ingår i: Agricultural Water Management. - : Elsevier BV. - 0378-3774. ; 275
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Tidskriftsartikel (refereegranskat)abstract
- Agroecosystem photosynthesis is key to coping with global climate change. In farmland where human activities are highly involved, the interaction between environmental factors and their influences on gross primary productivity (GPP) are insufficiently understood. Particularly, the irrigation and mulching in water-saving agriculture can alter the crop responses to environmental change. Based on eddy covariance measurements of maize fields under mulched drip irrigation (DM) and mulched border irrigation (BM) in arid areas of Northwest China from 2014 to 2018, we systematically studied the interaction between multiple environmental factors and their independent effects on GPP using structural equation modeling, partial correlation coefficient and decoupling analysis by bins. The top three factors exerting the largest total effects on the GPP were soil temperature (Ts), canopy temperature (Tc) and vapor pressure deficit (VPD), among which Ts (0.75) and Tc (0.66) had the largest total effect on GPP under DM and BM, respectively. The independent effects of Ts, soil water content (SWC) and VPD on GPP were different under the two irrigation methods. SWC after excluding the influence of Ts showed a negative effect on GPP under DM (−1.24 g Cm−2d−1), while a positive effect under BM (0.02 g Cm−2d−1). By contrast, SWC after excluding the influence of VPD showed a positive effect on GPP under DM (0.59 g Cm−2d−1), while a negative effect under BM (−0.05 g Cm−2d−1). Interestingly, higher Ts, lower SWC and higher VPD had the potential to increase GPP under the two irrigation methods. We also found that the total effects of irrigation and VPD as well as the indirect effects of environmental factors on GPP should not be ignored. Our study will provide important reference for dealing with the effect of high temperature and drought stress on agro-ecosystem GPP and evaluating the response of vegetation to environmental factors.
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| 14. |
- Wang, Chunyu, et al.
(författare)
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Modelling water and energy fluxes with an explicit representation of irrigation under mulch in a maize field
- 2022
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Ingår i: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923 .- 1873-2240. ; 326
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Tidskriftsartikel (refereegranskat)abstract
- Globally, water-saving irrigation plays a vital role in agricultural ecosystems to achieve sustainable food pro-duction under climate change. Irrigation under mulch (IUM) system has been widely used in modern agricultural ecosystems due to its high water use efficiency, but it remains unclear how each component of the water and energy processes responds to this agricultural management practice. Current modeling approaches are inade-quate in investigating the impacts of IUM management on water-energy balance, which have shown more complicated than non-mulched management. Therefore, this study provided an explicit simulation of water and energy fluxes in IUM system using a process-oriented ecosystem model-CoupModel and the three years of the eddy covariance (EC) measurements. Based on Monte Carlo and the multiple model performance evaluation criteria, most of the model sensitive parameters were well constrained and 32 potentially important parameters, e.g., iscovevap, the fraction of mulch coverage, were identified to characterize the impacts of plastic mulching on energy balance and water transport. After proper calibration, the coefficient of determination (R2) for measured and simulated soil temperature (T) and soil water content (SWC) was 0.79 and 0.60, respectively, and the R2 for T and SWC during the validation period were 0.91 and 0.71, respectively. Furthermore, we found that there was a strong coupling between the parameters of the water and energy processes, which would restrict the simulation results due to the correlation between the parameters and the evaluation indices. This study presented a sys-tematic model parameters calibration in the agricultural ecosystem implemented with IUM and provided with a more comprehensive understanding of the water and energy balance in cropland. These results would help agricultural model development with more detailed considerations of the water-saving management.
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| 15. |
- Wang, Chunyu, et al.
(författare)
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Water use efficiency control for a maize field under mulched drip irrigation
- 2023
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 857
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Tidskriftsartikel (refereegranskat)abstract
- Agricultural ecosystem water use efficiency (WUE) is an important indicator reflecting carbon-water coupling, but its control mechanisms in managed fields remain unclear. In order to reveal the influencing factors of WUE in the agricultural field under mulched drip irrigation (DM), we carried out the 8-year continuous observations in a maize field from Northwestern China. The structural equation model, relative importance analysis and principal component analysis were used to quantify the regulation effects of environmental and biological factors on WUE at different time scales, in different growth stages and under different hydrothermal conditions. The results showed that annual WUE varied between 2.18 g C Kg−1 H2O and 3.60 g C Kg−1 H2O, with a multi-year mean of 2.91 g C Kg−1 H2O. The total effects of air temperature on the daily WUE in the whole growth period, the vegetative growth stage, the warm and dry years, the cold and wet years, and the warm and wet years were the largest, with values of 0.61, 0.80, 0.70, 0.70 and 0.91 respectively. However, vapor pressure deficit and net radiation had the largest total effect in the cold and dry years (−0.63) and the reproductive growth stage (−0.49), respectively. Leaf biomass played a leading role in regulating the daily and interannual WUE, and the relative importance of leaf biomass to WUE in the vegetative growth stage was up to 75 %. In the warm and wet years, the relative importance of root biomass to WUE was 33 %, slightly higher than that of leaf biomass (31 %). At the same time, we found that Ta has the potential to increase WUE under future climate warming. Our results improve the understanding of carbon-water coupling mechanisms and provide important enlightenment on how crop ecosystems should adapt to future climate change.
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| 16. |
- Wang, Zhihua, et al.
(författare)
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Alkali metal release in thermochemical conversion of biomass and coal : Optical measurements and modeling
- 2024
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Ingår i: Progress in Energy and Combustion Science. - 0360-1285. ; 100
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Forskningsöversikt (refereegranskat)abstract
- Alkali metals, mainly K and Na, which are present in solid fuels such as biomass and coal, play an important role during their thermal conversion, e.g., in combustion or gasification. At high temperatures, alkali elements will be released in gas phase as alkali atoms, alkali chlorides, alkali hydroxides and alkali sulphates. In biomass/coal-fired boilers, the release of these alkali species can cause problems such as corrosion, slagging and fouling, threatening the safe operation of the facilities. The information on the release dynamic is important for developing proper models for alkali metal transformation in solid fuel combustion and gasification. Therefore, accurate quantitative measurements of the release of different alkali species during thermal-chemical conversion processes of biomass/coal are important. In this paper, we review literatures published over the last few decades in the field of quantitative optical measurements of alkali metals performed in combustion/gasification processes, and the release modeling based on those optical measurements. Firstly, the current situation of biomass and coal utilization is discussed, including the speciation of alkali metals in biomass/coal and their adverse effects on facilities. Secondly, requirements for optical measurements as well as several quantitative optical techniques are introduced including the general principles, typical setups, calibration methods and major advantages and drawbacks. In contrast to off-line techniques, these optical techniques provide nonintrusive measurements with high temporal and spatial resolution, which are indispensable for alkali release modeling. Furthermore, the alkali release behaviors based on optical measurements in thermochemical conversion processes are discussed. Based on the experimental results, the kinetic data for alkali release were summarized. Alkali release modeling was fulfilled relying on the knowledge of alkali release mechanisms and the kinetic data. In addition, simulations of alkali metal release with computational fluid dynamics during the biomass/coal combustion processes are also discussed, providing valuable information for industrial processes. Finally, typical examples of industrial applications of optical measurement methods in solid fuel thermochemical conversion processes as well as waste incineration and other processes are presented.
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| 17. |
- Yang, Danni, et al.
(författare)
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Drip irrigation improves spring wheat water productivity by reducing leaf area while increasing yield
- 2023
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Ingår i: European Journal of Agronomy. - : Elsevier BV. - 1161-0301. ; 143
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Tidskriftsartikel (refereegranskat)abstract
- To mitigate the climate change-induced water shortage and realize the sustainable development of agriculture, drip irrigation, a more efficient water-saving irrigation method, has been intensively implemented in most arid agricultural regions in the world. However, compared to traditional border irrigation, how drip irrigation affects the biophysical conditions in the cropland and how crops physiologically respond to changes in biophysical conditions in terms of water, heat and carbon exchange remain largely unknown. In view of the above situation, to reveal the mechanism of drip irrigation in improving spring wheat water productivity, paired field experiments based on drip irrigation and border irrigation were conducted to extensively monitor water and heat fluxes at a typical spring wheat field (Triticum aestivum L.) in Northwest China during 2017–2020. The results showed that drip irrigation improved yield by 10.3 % and crop water productivity (i.e., yield-to-evapotranspiration-ratio) by 15.6 %, but reduced LAI by 16.9 % in contrast with border irrigation. Under drip irrigation, the lateral development of spring wheat roots was promoted by higher soil temperature combined with frequent dry-wet alternation in the shallow soil layer (0–20 cm), which was the basis for efficient absorption of water and fertilizer, as well as efficient formation of photosynthate. Meanwhile, drip irrigation increased net radiation and decreased latent heat flux by inhibiting leaf growth, thereby increased sensible heat, causing a higher soil temperature (+1.10 ℃) and canopy temperature (+1.11 ℃). Further analysis proved that soil temperature was the key factor affecting yield formation. Based on the above conditions, the decrease in leaf distribution coefficient (−0.030) led to the decrease in evapotranspiration (−5.7 %) and the increase in ear distribution coefficient (+0.029). Therefore, drip irrigation emphasized the role of soil moisture in the soil-plant-atmosphere continuum, enhanced crop activity by increasing field temperature, especially soil temperature, and finally improved yield and water productivity via carbon reallocation. The study revealed the mechanism of drip irrigation for improving spring wheat yield, and would contribute to improving Earth system models in representing agricultural cropland ecosystems with drip irrigation and predicting the subsequent biophysical and biogeochemical feedbacks to climate change.
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