Proton exchange membrane fuel cells(PEMFCs)constitute a promising avenue for environmentally friendly power generation.However,the reliance on unsustainable platinum-based electrocatalysts used at the electrodes poses...Proton exchange membrane fuel cells(PEMFCs)constitute a promising avenue for environmentally friendly power generation.However,the reliance on unsustainable platinum-based electrocatalysts used at the electrodes poses challenges to the commercial viability of PEMFCs.Non-platinum group metal(non-PGM)alternatives,like nitrogen-coordinated transition metals in atomic dispersion(M–N–C catalysts),show significant potential.This work presents a comparative study of two distinct sets of Fe–N–C materials,prepared by pyrolyzing hybrid composites of polyaniline(PANI)and iron(Ⅱ)chloride on a hard template.One set uses bipyridine(BPy)as an additional nitrogen source and iron ligand,offering an innovative approach.The findings reveal that the choice of pyrolysis temperature and atmosphere influences the catalyst properties.The use of ammonia in pyrolysis emerges as a crucial parameter for promoting atomic dispersion of iron,as well as increasing surface area and porosity.The optimal catalyst,prepared using BPy and ammonia,exhibits a half-wave potential of 0.834 V in 0.5 M H_(2)SO_(4)(catalyst loading of 0.6 mg cm^(-2)),a mass activity exceeding 3 A g^(-1)and high stability in acidic electrolyte,positioning it as a promising non-PGM structure in the field.展开更多
The variations in the mechanical and magnetic properties of cold-rolled 20Mn23AlV non-magnetic structural steel after annealing at different temperatures were investigated.The microstructure and precipitation changes ...The variations in the mechanical and magnetic properties of cold-rolled 20Mn23AlV non-magnetic structural steel after annealing at different temperatures were investigated.The microstructure and precipitation changes during annealing were studied by optical microscopy,scanning electron microscopy,and transmission electron microscopy.The results show that recrystallization completed after annealing at 620℃,resulting in grain sizes of approximately 800 nm and the best combination of strength and plasticity.The yield-to-tensile ratio of the non-magnetic structural steel after cold rolling continuously decreases from low to high temperatures after annealing,with the highest value being 0.89 and the lowest value being 0.43,indicating a wide range of yield-to-tensile ratio adjustment.The introduction of numerous dislocations during cold rolling provided favorable nucleation sites for precipitation,leading to abundant precipitation of the fine second-phase V(C,N).The phase composition of the samples remained unchanged as single-phase austenite after annealing,and the relative permeability values were calculated to be less than 1.002,meeting the requirements for non-magnetic steel in terms of magnetic properties.展开更多
The microstructure of the 18R-type long period stacking ordered （LPSO） phase in Mg 97 Y 2 Zn 1 alloy was investigated by the first principles calculation. The arrangement rule of Zn and Y atoms in the LPSO structure...The microstructure of the 18R-type long period stacking ordered （LPSO） phase in Mg 97 Y 2 Zn 1 alloy was investigated by the first principles calculation. The arrangement rule of Zn and Y atoms in the LPSO structure is determined theoretically. The calculation results reveal that the additive atoms are firstly located in the fault layers at the two ends of the 18R-type LPSO structure, and then extend to fault layers in the interior, which is in good agreement with the experimental observations. This feature also implies the microstructural relationship between 18R and other LPSO structures. The cohesive energy and the formation heat indicate the dependence of the stability of 18R LPSO structure on contents of Y and Zn atoms. The calculated electronic structures reveal the underlying mechanism of microstructure and the stability of 18R LPSO structure.展开更多
Objective To examine the important roles of microRNAs （miRNAs） in regulating amphid structure and function, we performed a computational analysis for the genetic loci required for the sensory perception and their po...Objective To examine the important roles of microRNAs （miRNAs） in regulating amphid structure and function, we performed a computational analysis for the genetic loci required for the sensory perception and their possibly corresponding miRNAs in C. elegans. Methods Total 55 genetic loci required for the amphid structure and function were selected. Sequence alignment was combined with E value evaluation to investigate and identify the possible corresponding miRNAs. Results Total 30 genes among the 55 genetic loci selected have their possible corresponding regulatory miRNA（s）, and identified genes participate in the regulation of almost all aspects of amphid structure and function. In addition, our data suggest that both the amphid structure and the amphid functions might be regulated by a series of network signaling pathways. Moreover, the distribution of miRNAs along the 3＇ untranslated region （UTR） of these 30 genes exhibits different patterns. Conclusion We present the possible miRNA-mediated signaling pathways involved in the regulation of chemosensation and thermosensation by controlling the corresponding sensory neuron and interneuron functions. Our work will be useful for better understanding of the miRNA-mediated control of the chemotaxis and thermotaxis in C. elegans.展开更多
Traditionally governance structures are classified into ＂hierarchy or market＂ or ＂equity or non-equity.＂ However,such classifications may not be effective in characterizing all governance structures of research an...Traditionally governance structures are classified into ＂hierarchy or market＂ or ＂equity or non-equity.＂ However,such classifications may not be effective in characterizing all governance structures of research and development（R D） alliances.Therefore,the first objective of this study is to investigate why there exist different organizational governance structures in managing R D alliances;the second objective of this study is to give strategic advice in choosing appropriate forms with respect to various characteristics of R D alliances.Through the theoretical lens that integrate both transaction cost economics（TCE） and the resource-based view（RBV）,a model that focuses on six major factors is developed for determining governance structure choices,namely,technological uncertainty,cultural difference,asset specificity,technology complementarity,appropriability of the individual firm＇s know-how,and trust.An R D alliance with higher technological uncertainty,larger cultural differences,and greater concerns for protecting an individual＇s know-how is more likely to adopt non-integrated alliances as the governing structure.An R D alliance with a higher degree of asset-specificity,greater technology complementarity and greater trust among partnering organizations is more likely to adopt integrated alliances as the governing structure;an R D alliance in the face of lower technological uncertainty will tend to adopt integrated alliances.The more aligned the choice of the governance structure with its determinants,the better the R D alliance will perform,and vice versa.展开更多
研究了微肋管内R407C和R22的流动沸腾换热特性,采用威尔逊图解法对实验数据进行处理,主要分析实验工况、制冷剂物性、微肋管结构等变量的影响。结果表明:制冷剂R407C与R22与换热壁面之间的换热热阻均随热流密度、质流密度、干度、肋片...研究了微肋管内R407C和R22的流动沸腾换热特性,采用威尔逊图解法对实验数据进行处理,主要分析实验工况、制冷剂物性、微肋管结构等变量的影响。结果表明:制冷剂R407C与R22与换热壁面之间的换热热阻均随热流密度、质流密度、干度、肋片螺旋角等的增加而减小;由于制冷剂气液相密度比的差异性,R22传热系数比与R407C的高约18.5%—21.4%。选用关联式对微肋管内R407C流动沸腾换热特性进行预测评估,并对关联式预测精度随干度、质流密度等的变化趋势进行分析。在所选关联式内,Yu and Koyama关联式表现出最佳预测效果,其平均预测误差在±6.5%以内,且干度、质流密度对其预测精度的影响相近;而对于其它关联式,干度对关联式预测精度的影响比重普遍高于质流密度。展开更多
In many cases, seismic appraisal of existing structures is carried out by the two step method and seismic strengthening of R.C. frame structures is solved just based on rough calculation or experience of designers, wh...In many cases, seismic appraisal of existing structures is carried out by the two step method and seismic strengthening of R.C. frame structures is solved just based on rough calculation or experience of designers, which may lead to either lack of safety or too conservative in design. According to some related criteria and experts experience, a computer program is developed specially for seismic appraisal and seismic strengthening of R.C. frames (not more than 10 storeys) in this paper. Because the progra...展开更多
In order to enhance electrochemical properties of LiFePO4 （LFP） cathode materials, spherical porous nano/micro structured LFP/C cathode materials were synthesized by spray drying, followed by calcination. The result...In order to enhance electrochemical properties of LiFePO4 （LFP） cathode materials, spherical porous nano/micro structured LFP/C cathode materials were synthesized by spray drying, followed by calcination. The results show that the spherical precursors with the sizes of 0.5-5 μm can be completely converted to LFP/C when the calcination temperature is higher than 500 ℃. The LFP/C microspheres obtained at calcination temperature of 700 ℃ are composed of numerous particles with sizes of -20 nm, and have well-developed interconnected pore structure and large specific surface area of 28.77 mE/g. The specific discharge capacities of the LFP/C obtained at 700 ℃ are 162.43, 154.35 and 144.03 mA.h/g at 0.5C, 1C and 2C, respectively. Meanwhile, the capacity retentions can reach up to 100% after 50 cycles. The improved electrochemical properties of the materials are ascribed to a small Li＋ diffusion resistance and special structure of LFP/C microspheres.展开更多
A porous coral-structured Si/C composite as an anode material was fabricated by coating Si nanoparticles with a carbon layer from polyvinyl alcohol（PVA）, erosion of hydrofluoric（HF） acid, and secondary coating wit...A porous coral-structured Si/C composite as an anode material was fabricated by coating Si nanoparticles with a carbon layer from polyvinyl alcohol（PVA）, erosion of hydrofluoric（HF） acid, and secondary coating with pitch. Three samples with different pitch contents of 30%, 40% and 50% were synthesized. The composition and morphology of the composites were characterized by X-ray diffractometry（XRD） and scanning electron microscopy（SEM）, respectively, and the properties were tested by electrochemical measurements. The results indicated that the composites showed obviously enhanced electrochemical performance compared with that without secondary carbon coating. The second discharge capacity of the composite was 773 m A·h/g at a current density of 100 m A/g, and still retained 669 m A·h/g after 60 cycles with a small capacity fade of less than 0.23%/cycle, while the content of secondary carbon source of pitch was set at 40%. Therefore, the cycle stability of the composite could be excellently improved by regulating carbon content of secondary coating.展开更多
The samples of the C-S-H series were synthesized by hydrothermal reaction of fumed silica, CaO and deionized water at initial C/S ratios between 1.0-1.7. Phase composition and structural and morphology characteristics...The samples of the C-S-H series were synthesized by hydrothermal reaction of fumed silica, CaO and deionized water at initial C/S ratios between 1.0-1.7. Phase composition and structural and morphology characteristics of C-S-H samples were analyzed by XRD, IR and SEM. The experimental results showed that the d-spacing of （002）, （110） and （020） decreased, the d-spacing of （200） increased, and the d-spacing of （310） varied randomly, the polymerization of silica tetrahedra of C-S-H decreased, and morphology of C-S-H samples varied from sheet shapes to long reticular fibers as C/S ratio increased.展开更多
Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by ...Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by the deposition of Zr and Si atoms on the shallow surface of the porous C/C composites.Ablation analysis showed that the defects in the coatings originate from the boundary between the ZrC and holes created by the consumption of SiC at 2500℃. After ablation for 200 s at 3000℃, a dense ZrO2 layer formed on the coating surface, and the defects were sealed owing to the continuous supply of ablative components. The mass and line ablation rates of the Zr C-SiC coatings were-0.46 ± 0.15 mg cm^-2·s^-1 and-1.00± 0.04 μm s^-1, respectively.展开更多
基金funding from the Hellenic Foundation for Research and Innovation(HFRI)under grant agreement No 3655.
文摘Proton exchange membrane fuel cells(PEMFCs)constitute a promising avenue for environmentally friendly power generation.However,the reliance on unsustainable platinum-based electrocatalysts used at the electrodes poses challenges to the commercial viability of PEMFCs.Non-platinum group metal(non-PGM)alternatives,like nitrogen-coordinated transition metals in atomic dispersion(M–N–C catalysts),show significant potential.This work presents a comparative study of two distinct sets of Fe–N–C materials,prepared by pyrolyzing hybrid composites of polyaniline(PANI)and iron(Ⅱ)chloride on a hard template.One set uses bipyridine(BPy)as an additional nitrogen source and iron ligand,offering an innovative approach.The findings reveal that the choice of pyrolysis temperature and atmosphere influences the catalyst properties.The use of ammonia in pyrolysis emerges as a crucial parameter for promoting atomic dispersion of iron,as well as increasing surface area and porosity.The optimal catalyst,prepared using BPy and ammonia,exhibits a half-wave potential of 0.834 V in 0.5 M H_(2)SO_(4)(catalyst loading of 0.6 mg cm^(-2)),a mass activity exceeding 3 A g^(-1)and high stability in acidic electrolyte,positioning it as a promising non-PGM structure in the field.
基金support from the Gansu Province Science and Technology Major Project(22ZD6GA008)Commissioner for Science,Technology Program of China Gansu Province(23CXA0013)+1 种基金National Natural Science Foundation of China(NSFC)(52061022)Jiayuguan City Science and Technology Major Project of China Gansu Province(22-02).
文摘The variations in the mechanical and magnetic properties of cold-rolled 20Mn23AlV non-magnetic structural steel after annealing at different temperatures were investigated.The microstructure and precipitation changes during annealing were studied by optical microscopy,scanning electron microscopy,and transmission electron microscopy.The results show that recrystallization completed after annealing at 620℃,resulting in grain sizes of approximately 800 nm and the best combination of strength and plasticity.The yield-to-tensile ratio of the non-magnetic structural steel after cold rolling continuously decreases from low to high temperatures after annealing,with the highest value being 0.89 and the lowest value being 0.43,indicating a wide range of yield-to-tensile ratio adjustment.The introduction of numerous dislocations during cold rolling provided favorable nucleation sites for precipitation,leading to abundant precipitation of the fine second-phase V(C,N).The phase composition of the samples remained unchanged as single-phase austenite after annealing,and the relative permeability values were calculated to be less than 1.002,meeting the requirements for non-magnetic steel in terms of magnetic properties.
基金Projects(50861002,51071053)supported by the National Natural Science Foundation of ChinaProject(0991051)supported by NaturalScience Foundation of Guangxi Province,China+1 种基金Project(KF0803)supported by Open Project of Key Laboratory of Materials Design and Preparation Technology of Hunan Province,ChinaProject(X071117)supported by Scientific Research Foundation of Guangxi University,China
文摘The microstructure of the 18R-type long period stacking ordered （LPSO） phase in Mg 97 Y 2 Zn 1 alloy was investigated by the first principles calculation. The arrangement rule of Zn and Y atoms in the LPSO structure is determined theoretically. The calculation results reveal that the additive atoms are firstly located in the fault layers at the two ends of the 18R-type LPSO structure, and then extend to fault layers in the interior, which is in good agreement with the experimental observations. This feature also implies the microstructural relationship between 18R and other LPSO structures. The cohesive energy and the formation heat indicate the dependence of the stability of 18R LPSO structure on contents of Y and Zn atoms. The calculated electronic structures reveal the underlying mechanism of microstructure and the stability of 18R LPSO structure.
文摘Objective To examine the important roles of microRNAs （miRNAs） in regulating amphid structure and function, we performed a computational analysis for the genetic loci required for the sensory perception and their possibly corresponding miRNAs in C. elegans. Methods Total 55 genetic loci required for the amphid structure and function were selected. Sequence alignment was combined with E value evaluation to investigate and identify the possible corresponding miRNAs. Results Total 30 genes among the 55 genetic loci selected have their possible corresponding regulatory miRNA（s）, and identified genes participate in the regulation of almost all aspects of amphid structure and function. In addition, our data suggest that both the amphid structure and the amphid functions might be regulated by a series of network signaling pathways. Moreover, the distribution of miRNAs along the 3＇ untranslated region （UTR） of these 30 genes exhibits different patterns. Conclusion We present the possible miRNA-mediated signaling pathways involved in the regulation of chemosensation and thermosensation by controlling the corresponding sensory neuron and interneuron functions. Our work will be useful for better understanding of the miRNA-mediated control of the chemotaxis and thermotaxis in C. elegans.
基金The Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Traditionally governance structures are classified into ＂hierarchy or market＂ or ＂equity or non-equity.＂ However,such classifications may not be effective in characterizing all governance structures of research and development（R D） alliances.Therefore,the first objective of this study is to investigate why there exist different organizational governance structures in managing R D alliances;the second objective of this study is to give strategic advice in choosing appropriate forms with respect to various characteristics of R D alliances.Through the theoretical lens that integrate both transaction cost economics（TCE） and the resource-based view（RBV）,a model that focuses on six major factors is developed for determining governance structure choices,namely,technological uncertainty,cultural difference,asset specificity,technology complementarity,appropriability of the individual firm＇s know-how,and trust.An R D alliance with higher technological uncertainty,larger cultural differences,and greater concerns for protecting an individual＇s know-how is more likely to adopt non-integrated alliances as the governing structure.An R D alliance with a higher degree of asset-specificity,greater technology complementarity and greater trust among partnering organizations is more likely to adopt integrated alliances as the governing structure;an R D alliance in the face of lower technological uncertainty will tend to adopt integrated alliances.The more aligned the choice of the governance structure with its determinants,the better the R D alliance will perform,and vice versa.
文摘研究了微肋管内R407C和R22的流动沸腾换热特性,采用威尔逊图解法对实验数据进行处理,主要分析实验工况、制冷剂物性、微肋管结构等变量的影响。结果表明:制冷剂R407C与R22与换热壁面之间的换热热阻均随热流密度、质流密度、干度、肋片螺旋角等的增加而减小;由于制冷剂气液相密度比的差异性,R22传热系数比与R407C的高约18.5%—21.4%。选用关联式对微肋管内R407C流动沸腾换热特性进行预测评估,并对关联式预测精度随干度、质流密度等的变化趋势进行分析。在所选关联式内,Yu and Koyama关联式表现出最佳预测效果,其平均预测误差在±6.5%以内,且干度、质流密度对其预测精度的影响相近;而对于其它关联式,干度对关联式预测精度的影响比重普遍高于质流密度。
文摘In many cases, seismic appraisal of existing structures is carried out by the two step method and seismic strengthening of R.C. frame structures is solved just based on rough calculation or experience of designers, which may lead to either lack of safety or too conservative in design. According to some related criteria and experts experience, a computer program is developed specially for seismic appraisal and seismic strengthening of R.C. frames (not more than 10 storeys) in this paper. Because the progra...
基金Project(2013AA050901)supported by the National High-tech Research and Development Program of China
文摘In order to enhance electrochemical properties of LiFePO4 （LFP） cathode materials, spherical porous nano/micro structured LFP/C cathode materials were synthesized by spray drying, followed by calcination. The results show that the spherical precursors with the sizes of 0.5-5 μm can be completely converted to LFP/C when the calcination temperature is higher than 500 ℃. The LFP/C microspheres obtained at calcination temperature of 700 ℃ are composed of numerous particles with sizes of -20 nm, and have well-developed interconnected pore structure and large specific surface area of 28.77 mE/g. The specific discharge capacities of the LFP/C obtained at 700 ℃ are 162.43, 154.35 and 144.03 mA.h/g at 0.5C, 1C and 2C, respectively. Meanwhile, the capacity retentions can reach up to 100% after 50 cycles. The improved electrochemical properties of the materials are ascribed to a small Li＋ diffusion resistance and special structure of LFP/C microspheres.
基金Project(11204090)supported by the National Natural Science Foundation of ChinaProject(2013KJCX0050)supported by the Department of Education of Guangdong Province+6 种基金ChinaProjects(2014B0404040672014A0404010052015A0404040432015A090905003201508030033)supported by the Scientific and Technological Plan of Guangdong Province and Guangzhou CityChina
文摘A porous coral-structured Si/C composite as an anode material was fabricated by coating Si nanoparticles with a carbon layer from polyvinyl alcohol（PVA）, erosion of hydrofluoric（HF） acid, and secondary coating with pitch. Three samples with different pitch contents of 30%, 40% and 50% were synthesized. The composition and morphology of the composites were characterized by X-ray diffractometry（XRD） and scanning electron microscopy（SEM）, respectively, and the properties were tested by electrochemical measurements. The results indicated that the composites showed obviously enhanced electrochemical performance compared with that without secondary carbon coating. The second discharge capacity of the composite was 773 m A·h/g at a current density of 100 m A/g, and still retained 669 m A·h/g after 60 cycles with a small capacity fade of less than 0.23%/cycle, while the content of secondary carbon source of pitch was set at 40%. Therefore, the cycle stability of the composite could be excellently improved by regulating carbon content of secondary coating.
基金Funded by the National Basic Research Program of China (973 Program) (No. 2009CB623201)the National Natural Science Foundation of China (No.51072150)
文摘The samples of the C-S-H series were synthesized by hydrothermal reaction of fumed silica, CaO and deionized water at initial C/S ratios between 1.0-1.7. Phase composition and structural and morphology characteristics of C-S-H samples were analyzed by XRD, IR and SEM. The experimental results showed that the d-spacing of （002）, （110） and （020） decreased, the d-spacing of （200） increased, and the d-spacing of （310） varied randomly, the polymerization of silica tetrahedra of C-S-H decreased, and morphology of C-S-H samples varied from sheet shapes to long reticular fibers as C/S ratio increased.
基金supported by National Science Foundation of China (No. 51405522)the self-fund of State Key Laboratory for Powder Metallurgy (PM-CSU-2015-03)
文摘Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by the deposition of Zr and Si atoms on the shallow surface of the porous C/C composites.Ablation analysis showed that the defects in the coatings originate from the boundary between the ZrC and holes created by the consumption of SiC at 2500℃. After ablation for 200 s at 3000℃, a dense ZrO2 layer formed on the coating surface, and the defects were sealed owing to the continuous supply of ablative components. The mass and line ablation rates of the Zr C-SiC coatings were-0.46 ± 0.15 mg cm^-2·s^-1 and-1.00± 0.04 μm s^-1, respectively.
