1.Challenges circular methane energy systems In recent decades,methane-based energy systems have rapidly gained traction across the globe because of the increasing availability of low-cost methane production capacity....1.Challenges circular methane energy systems In recent decades,methane-based energy systems have rapidly gained traction across the globe because of the increasing availability of low-cost methane production capacity.However,fossil methane production and combustion lead to large greenhouse gas emissions,contributing to climate change[1].展开更多
In this work, the zeolite-Y was ion-exchanged by introducing silver cations into the framework of microsized nano-porous sodium zeolite-Y using a liquid-phase ion exchanged method. The Ag+ion-exchanged zeolite, was th...In this work, the zeolite-Y was ion-exchanged by introducing silver cations into the framework of microsized nano-porous sodium zeolite-Y using a liquid-phase ion exchanged method. The Ag+ion-exchanged zeolite, was then embedded into the Matrimid5218 matrix to form novel mixed matrix membranes(MMMs). The particles and MMMs were characterized by ultraviolet-visible diffuse reflectance spectroscopy(UV–vis DRS), N2adsorption–desorption isotherm, X-ray diffraction(XRD), Fourier transform infrared(FTIR) and scanning electron microscopy(SEM). Furthermore, the effects of filler content(0–20wt%) on pure and mixed gas experiments, feed pressure(2–20 bar) and operating temperature(35–75 oC)on CO2/CH4transport properties of Matrimid/Ag Y MMMs were considered. Characterization results confirmed an appropriate ion-exchange treatment of the zeolites. The SEM results confirmed the superior interfacial adhesion between polymer and zeolites, particularly in the case of Matrimid/Ag Y membranes.This is due to the proper silverous zeolite/Matrimid functional groups’ interactions. The gas permeation results showed that the CO2permeability increased about 123%, from 8.34 Barrer for pure Matrimid to18.62 Barrer for Matrimid/Ag Y(15 wt%). The CO2/CH4selectivity was improved about 66%, from 36.3 for Matrimid to 60.1 for Matrimid/Ag Y(15 wt%). The privileged gas separation performance of Matrimid/Ag Y(15 wt%) was the result of a combined effect of facilitated transport mechanism of Ag+ions as well as the intrinsic surface diffusion mechanism of Y-type zeolite. In order to survey the possibility of using the developed MMMs in industry, the CO2-induced plasticization effect and mixed gas experiment were accomplished. It was deduced that the fabricated MMMs could maintain the superior performance in actual operating conditions.展开更多
A methodology integrating correlation,regression(MLR),machine learning(ML),and pattern analysis of long-term weekly net ecosystem exchange(NEE)datasets are applied to four deciduous broadleaf forest(DBF)sites forming ...A methodology integrating correlation,regression(MLR),machine learning(ML),and pattern analysis of long-term weekly net ecosystem exchange(NEE)datasets are applied to four deciduous broadleaf forest(DBF)sites forming part of the AmeriFlux(FLUXNET2015)database.Such analysis effectively characterizes and distinguishes those DBF sites for which long-term NEE patterns can be accurately predicted using the recorded environmental variables,from those sites cannot be so delineated.Comparisons of twelve NEE prediction models(5 MLR;7 ML),using multi-fold cross-validation analysis,reveal that support vector regression generates the most accurate and reliable predictions for each site considered,based on fits involving between 16 and 24 available environmental variables.SVR can accurately predict NEE for datasets for DBF sites US-MMS and US-MOz,but fail to reliably do so for sites CA-Cbo and MX-Tes.For the latter two sites the predicted versus recorded NEE weekly data follow a Y≠X pattern and are characterized by rapid fluctuations between low and high NEE values across leaf-on seasonal periods.Variable influences on NEE,determined by their importance to MLR and ML model solutions,identify distinctive sets of the most and least influential variables for each site studied.Such information is valuable for monitoring and modelling the likely impacts of changing climate on the ability of these sites to serve as long-term carbon sinks.The periodically oscillating NEE weekly patterns distinguished for sites CA-Cbo and MX-Tes are not readily explained in terms of the currently recorded environmental variables.More detailed analysis of the biological processes at work in the forest understory and soil at these sites are recommended to determine additional suitable variables to measure that might better explain such fluctuations.展开更多
To improve the coefficient of performance （COP） of CO2 transcritical reverse cycle and determine the most efficient cycle, comparison analysis on （single-and） two-stage CO2 transcritical cycles with internal heat ...To improve the coefficient of performance （COP） of CO2 transcritical reverse cycle and determine the most efficient cycle, comparison analysis on （single-and） two-stage CO2 transcritical cycles with internal heat exchanger （IHX） or expander is presented adopting the principle of thermodynamics. Results indicate that the COP of four cycles,namely single-stage compression with IHX （SI）, single-stage compression with expander （SE）, two-stage compression with IHX （TI） and two-stage compression with expander （TE）, can be ranged as TE>SE>TI>SI. It presents that adopting an expander to recover expansion power is the primary method to improve the COP of CO2 transcritical reverse cycle if the efficiency of the expander is up to a certain value. Under supposed operating condition, where the outlet temperature of gas cooler is 35 ℃ and the evaporating temperature is 5 ℃, the COP of TE cycle is about 4200 higher than that of SI cycle when the expander efficiency is 0.6 and the degree of superheat of IHX is 15 ℃. Therefore TE cycle is the most recommendatory one and it is better to adopt TE in those high-cooling capacity systems because its technology cost will be higher.展开更多
The comparison between the carbon isotope and the index of ring width of a pine disc from the Tuomuer Peak region in Xinjiang shows that the effects of climate changes on the tree-ring growth and carbon isotopic fract...The comparison between the carbon isotope and the index of ring width of a pine disc from the Tuomuer Peak region in Xinjiang shows that the effects of climate changes on the tree-ring growth and carbon isotopic fractionation varies with time. The reason is probably relative to the characters of climate changes and adaptability of the tree-ring growth to climate changes. The relationships between the atmospheric CO2 level and the revised δ13Cair by the tree-ring carbon isotope indicate that the carbon cycle is not in a steady state, but under a stage-change condition in this area. It also can be concluded that the ratio of CO2 from the terrestrial eco-system has increased, and the flux of CO2 exchange between the atmosphere and the biosphere was gradually increasing over the past century. In addition, the results also confirm the validity and superiority of the carbon isotope to the research of the water-use efficiency.展开更多
基金funding from the European Research Council (ERC)under grant agreement no.834134 (WATUSO)VLAIO for Moonshot funding (ARCLATH,No.HBC.2019.0110 and ARCLATH2,No.HBC.2021.0254)+3 种基金supported by the Flemish Government as an international research infrastructure (I001321N)infrastructure support by Department EWI via the Hermes Fund (AH.2016.134)the Hercules Foundation (AKUL/13/21)FWO Vlaanderen for an FWO-SB fellowship。
文摘1.Challenges circular methane energy systems In recent decades,methane-based energy systems have rapidly gained traction across the globe because of the increasing availability of low-cost methane production capacity.However,fossil methane production and combustion lead to large greenhouse gas emissions,contributing to climate change[1].
文摘In this work, the zeolite-Y was ion-exchanged by introducing silver cations into the framework of microsized nano-porous sodium zeolite-Y using a liquid-phase ion exchanged method. The Ag+ion-exchanged zeolite, was then embedded into the Matrimid5218 matrix to form novel mixed matrix membranes(MMMs). The particles and MMMs were characterized by ultraviolet-visible diffuse reflectance spectroscopy(UV–vis DRS), N2adsorption–desorption isotherm, X-ray diffraction(XRD), Fourier transform infrared(FTIR) and scanning electron microscopy(SEM). Furthermore, the effects of filler content(0–20wt%) on pure and mixed gas experiments, feed pressure(2–20 bar) and operating temperature(35–75 oC)on CO2/CH4transport properties of Matrimid/Ag Y MMMs were considered. Characterization results confirmed an appropriate ion-exchange treatment of the zeolites. The SEM results confirmed the superior interfacial adhesion between polymer and zeolites, particularly in the case of Matrimid/Ag Y membranes.This is due to the proper silverous zeolite/Matrimid functional groups’ interactions. The gas permeation results showed that the CO2permeability increased about 123%, from 8.34 Barrer for pure Matrimid to18.62 Barrer for Matrimid/Ag Y(15 wt%). The CO2/CH4selectivity was improved about 66%, from 36.3 for Matrimid to 60.1 for Matrimid/Ag Y(15 wt%). The privileged gas separation performance of Matrimid/Ag Y(15 wt%) was the result of a combined effect of facilitated transport mechanism of Ag+ions as well as the intrinsic surface diffusion mechanism of Y-type zeolite. In order to survey the possibility of using the developed MMMs in industry, the CO2-induced plasticization effect and mixed gas experiment were accomplished. It was deduced that the fabricated MMMs could maintain the superior performance in actual operating conditions.
文摘A methodology integrating correlation,regression(MLR),machine learning(ML),and pattern analysis of long-term weekly net ecosystem exchange(NEE)datasets are applied to four deciduous broadleaf forest(DBF)sites forming part of the AmeriFlux(FLUXNET2015)database.Such analysis effectively characterizes and distinguishes those DBF sites for which long-term NEE patterns can be accurately predicted using the recorded environmental variables,from those sites cannot be so delineated.Comparisons of twelve NEE prediction models(5 MLR;7 ML),using multi-fold cross-validation analysis,reveal that support vector regression generates the most accurate and reliable predictions for each site considered,based on fits involving between 16 and 24 available environmental variables.SVR can accurately predict NEE for datasets for DBF sites US-MMS and US-MOz,but fail to reliably do so for sites CA-Cbo and MX-Tes.For the latter two sites the predicted versus recorded NEE weekly data follow a Y≠X pattern and are characterized by rapid fluctuations between low and high NEE values across leaf-on seasonal periods.Variable influences on NEE,determined by their importance to MLR and ML model solutions,identify distinctive sets of the most and least influential variables for each site studied.Such information is valuable for monitoring and modelling the likely impacts of changing climate on the ability of these sites to serve as long-term carbon sinks.The periodically oscillating NEE weekly patterns distinguished for sites CA-Cbo and MX-Tes are not readily explained in terms of the currently recorded environmental variables.More detailed analysis of the biological processes at work in the forest understory and soil at these sites are recommended to determine additional suitable variables to measure that might better explain such fluctuations.
文摘To improve the coefficient of performance （COP） of CO2 transcritical reverse cycle and determine the most efficient cycle, comparison analysis on （single-and） two-stage CO2 transcritical cycles with internal heat exchanger （IHX） or expander is presented adopting the principle of thermodynamics. Results indicate that the COP of four cycles,namely single-stage compression with IHX （SI）, single-stage compression with expander （SE）, two-stage compression with IHX （TI） and two-stage compression with expander （TE）, can be ranged as TE>SE>TI>SI. It presents that adopting an expander to recover expansion power is the primary method to improve the COP of CO2 transcritical reverse cycle if the efficiency of the expander is up to a certain value. Under supposed operating condition, where the outlet temperature of gas cooler is 35 ℃ and the evaporating temperature is 5 ℃, the COP of TE cycle is about 4200 higher than that of SI cycle when the expander efficiency is 0.6 and the degree of superheat of IHX is 15 ℃. Therefore TE cycle is the most recommendatory one and it is better to adopt TE in those high-cooling capacity systems because its technology cost will be higher.
基金The work was supported by the National NaturalScience Foundation of China (Grant Nos.49333040 and 49903007).
文摘The comparison between the carbon isotope and the index of ring width of a pine disc from the Tuomuer Peak region in Xinjiang shows that the effects of climate changes on the tree-ring growth and carbon isotopic fractionation varies with time. The reason is probably relative to the characters of climate changes and adaptability of the tree-ring growth to climate changes. The relationships between the atmospheric CO2 level and the revised δ13Cair by the tree-ring carbon isotope indicate that the carbon cycle is not in a steady state, but under a stage-change condition in this area. It also can be concluded that the ratio of CO2 from the terrestrial eco-system has increased, and the flux of CO2 exchange between the atmosphere and the biosphere was gradually increasing over the past century. In addition, the results also confirm the validity and superiority of the carbon isotope to the research of the water-use efficiency.
