Developing effective iron-incorporated zeolites and determining their active centers for the direct oxidation of CH_4 to oxygenates have remained challenging topics so far.In this paper,we successfully prepare the hig...Developing effective iron-incorporated zeolites and determining their active centers for the direct oxidation of CH_4 to oxygenates have remained challenging topics so far.In this paper,we successfully prepare the highly-dispersed iron supported Y zeolites by a facile solid-state ion-exchange method with ferrocene,which was conducted under water-free conditions followed by a series of calcination.Moreover,extra-framework dinuclear Fe^(2+)complexes are identified as so-called activeα-iron sites on zeolites.ICP-OES,N_2 adsorption–desorption test,X-ray diffraction,solid-state^(27)Al NMR,N_2O titration,TEM,EPR and^(57)Fe M?ssbauer spectra were carried out to characterize properties of sample structure,acid sites,as well as the supported iron species.Characterization results indicate that high-temperature treatments have no effect on the typical structure feature of zeolites.Compared with catalysts synthesized by conventional impregnation,the samples prepared by the facile approach possess abundant dinuclear Fe^(2+)complexes but no Fe_2O_3 bulks and show weak acidity.These lead to a higher oxygenate selectivity in CH_4 oxidation to oxygenates.Remarkably,the oxygenate(HCHO and CH_3OH)selectivity of 6.5% at 375°C can be eventually obtained.展开更多
This paper discusses one of the contemporary challenging issues--it is the challenge of e-commerce to the sovereignty of the state, where governments are unable to implement their own laws on disputed cases resulting ...This paper discusses one of the contemporary challenging issues--it is the challenge of e-commerce to the sovereignty of the state, where governments are unable to implement their own laws on disputed cases resulting from trans-border e-commerce interactions. The objective of the current research is to draw attention to the impact of international characteristics of e-commerce on the sovereignty of state, and to identify the factors affecting this sovereignty. The issue of the dynamieity of time and place will be taken into consideration, where activities carded out over the internet are characterized by their cross-border dimension. Based on real e-commerce case studies disputed on international level, this paper will draw on the legal perspective of cyberspace, identifying the relationship between cyberspace and state sovereignty, and outlining the mechanisms by which cyberspace could cross borders and the territory of the state despite all the precautions taken by the state to protect its sovereignty.展开更多
The spectroscopy characteristics and the fluorescence lifetime for the chloroplasts isolated from the pseudo ginseng, water hyacinth and spinach plant leaves have been studied by absorption spectra, low temperature st...The spectroscopy characteristics and the fluorescence lifetime for the chloroplasts isolated from the pseudo ginseng, water hyacinth and spinach plant leaves have been studied by absorption spectra, low temperature steady-state fluorescence spectroscopy and single photon counting measurement under the same conditions and by the same methods. The similarity of the absorption spectra for the chloroplasts at room temperature suggests that different plants can efficiently absorb light of the same wavelength. The fluorescence decays in PS II measured at the natural QA state for the chloroplasts have been fitted by a three-exponential kinetic model. The three fluorescence lifetimes are 30, 274 and 805 ps for the pseudo ginseng chloroplast; 138, 521 and 1494 ps for the water hyacinth chloroplast; 197, 465 and 1459 ps for the spinach chloroplast, respectively. The slow lifetime fluorescence component is assigned to a collection of associated light harvesting Chl a/b proteins, the fast lifetime component to the reaction center of PS II and the middle lifetime component to the delay fluorescence of recombination of P+ 680 and Pheo-. The excitation energy conversion efficiency(η) in PS II RC is defined and calculated on the basis of the 20 ps electron transfer time constant model, 60%, 87% and 91% for the pseudo ginseng, water hyacinth and spinach chloroplasts, respectively. This interesting result is in unconformity with what is assumed to be 100% efficiency in PS II RC. Our result in this work stands in line with the 20 ps electron transfer time constant in PS II rather sound and the water hyacinth plant grows slower than the spinach plant does as envisaged on the efficiency. But, our results predict that those plants can perform highly efficient transfer of photo-excitation energy from the light-harvesting pigment system to the reaction center (closely to 100%). The conclusion contained in this paper reveals the plant growth characteristics expressed in the primary processes of photosynthesis and a relationship between a plant growing rate and its spectroscopy characteristics and fluorescence lifetimes, namely, the slower a plant grows, the less excitation energy conversation efficiency used might be anticipated.展开更多
Since silicon is limited by its physical properties,it is challenging and important to find candidate materials for high performance electronic devices.Two-dimensional（2D）semiconductor materials have attracted drama...Since silicon is limited by its physical properties,it is challenging and important to find candidate materials for high performance electronic devices.Two-dimensional（2D）semiconductor materials have attracted dramatically increasing interest due to their unique physical,展开更多
基金Support by the National Key R&D Program of China(2016YFA0202900)the National Natural Science Foundation of China(21622606)+2 种基金the Natural Science Foundation of Zhejiang Province(LR18B060001)Basic Research Project of Sinopec Group(415025)the Fundamental Research Funds for the Central Universities
文摘Developing effective iron-incorporated zeolites and determining their active centers for the direct oxidation of CH_4 to oxygenates have remained challenging topics so far.In this paper,we successfully prepare the highly-dispersed iron supported Y zeolites by a facile solid-state ion-exchange method with ferrocene,which was conducted under water-free conditions followed by a series of calcination.Moreover,extra-framework dinuclear Fe^(2+)complexes are identified as so-called activeα-iron sites on zeolites.ICP-OES,N_2 adsorption–desorption test,X-ray diffraction,solid-state^(27)Al NMR,N_2O titration,TEM,EPR and^(57)Fe M?ssbauer spectra were carried out to characterize properties of sample structure,acid sites,as well as the supported iron species.Characterization results indicate that high-temperature treatments have no effect on the typical structure feature of zeolites.Compared with catalysts synthesized by conventional impregnation,the samples prepared by the facile approach possess abundant dinuclear Fe^(2+)complexes but no Fe_2O_3 bulks and show weak acidity.These lead to a higher oxygenate selectivity in CH_4 oxidation to oxygenates.Remarkably,the oxygenate(HCHO and CH_3OH)selectivity of 6.5% at 375°C can be eventually obtained.
文摘This paper discusses one of the contemporary challenging issues--it is the challenge of e-commerce to the sovereignty of the state, where governments are unable to implement their own laws on disputed cases resulting from trans-border e-commerce interactions. The objective of the current research is to draw attention to the impact of international characteristics of e-commerce on the sovereignty of state, and to identify the factors affecting this sovereignty. The issue of the dynamieity of time and place will be taken into consideration, where activities carded out over the internet are characterized by their cross-border dimension. Based on real e-commerce case studies disputed on international level, this paper will draw on the legal perspective of cyberspace, identifying the relationship between cyberspace and state sovereignty, and outlining the mechanisms by which cyberspace could cross borders and the territory of the state despite all the precautions taken by the state to protect its sovereignty.
基金Acknowledgements The authors thank Prof. Xia Zongju in Peking University and Prof. Peng Hangcheng in the Institute of Biophysics of Chinese Academy of Sciences for their help in carrying out the single photon counting experiment, and Dr. Lin Su in Photos
文摘The spectroscopy characteristics and the fluorescence lifetime for the chloroplasts isolated from the pseudo ginseng, water hyacinth and spinach plant leaves have been studied by absorption spectra, low temperature steady-state fluorescence spectroscopy and single photon counting measurement under the same conditions and by the same methods. The similarity of the absorption spectra for the chloroplasts at room temperature suggests that different plants can efficiently absorb light of the same wavelength. The fluorescence decays in PS II measured at the natural QA state for the chloroplasts have been fitted by a three-exponential kinetic model. The three fluorescence lifetimes are 30, 274 and 805 ps for the pseudo ginseng chloroplast; 138, 521 and 1494 ps for the water hyacinth chloroplast; 197, 465 and 1459 ps for the spinach chloroplast, respectively. The slow lifetime fluorescence component is assigned to a collection of associated light harvesting Chl a/b proteins, the fast lifetime component to the reaction center of PS II and the middle lifetime component to the delay fluorescence of recombination of P+ 680 and Pheo-. The excitation energy conversion efficiency(η) in PS II RC is defined and calculated on the basis of the 20 ps electron transfer time constant model, 60%, 87% and 91% for the pseudo ginseng, water hyacinth and spinach chloroplasts, respectively. This interesting result is in unconformity with what is assumed to be 100% efficiency in PS II RC. Our result in this work stands in line with the 20 ps electron transfer time constant in PS II rather sound and the water hyacinth plant grows slower than the spinach plant does as envisaged on the efficiency. But, our results predict that those plants can perform highly efficient transfer of photo-excitation energy from the light-harvesting pigment system to the reaction center (closely to 100%). The conclusion contained in this paper reveals the plant growth characteristics expressed in the primary processes of photosynthesis and a relationship between a plant growing rate and its spectroscopy characteristics and fluorescence lifetimes, namely, the slower a plant grows, the less excitation energy conversation efficiency used might be anticipated.
基金supported by the National Key Basic Research Program of China(Grant No.2013CB632900)National Natural Science Foundation of China(Grant Nos.61390502&21373068)+1 种基金the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(Grant No.51521003)Self-Planned Task of State Key Laboratory of Robotics and System(HIT)(Grant No.SKLRS201607B)
文摘Since silicon is limited by its physical properties,it is challenging and important to find candidate materials for high performance electronic devices.Two-dimensional（2D）semiconductor materials have attracted dramatically increasing interest due to their unique physical,
