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Polyimide covalent organic frameworks as efficient solid-state Li^(+) electrolytes

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Science China Chemistry 2024年第5期67卷 1647-1652页

作者： Xu liu Shi Wang Siqi liu chengfang liu Xiangchun Li Jian Wu Dazhi Li Shihao Xu Chongyang liu Wen-Yong Lai State Key Laboratory of Organic Electronics and Information Displays(SKLOEID) Institute of Advanced Materials(IAM)School of Chemistry and Life SciencesNanjing University of Posts&TelecommunicationsNanjing 210023China

Covalent organic frameworks(COFs) are attractive porous crystalline materials with extremely high stability, easy functionalization, and open channels, which are expected to be unique ion conductors/transporters in lithium ion batteries(LIBs). Despite recent advances, low ion conductivity and low transference number, resulting in low charging/discharging rate, low energy density, and short battery life, are the main issues that limit their direct application as solid electrolytes in LIBs. Here, we designed and synthesized a novel polyimide COF, namely, TAPA-PDI-COF, with abundant C=O groups, which has been successfully employed as high-performance solid electrolytes by doping TAPA-PDI-COF and succinonitrile(SN). Both the well-defined nanochannels of COFs and SN confined in the well-aligned channels restricted the free migration of anions, while C=O on COFs and CN groups of SN enhanced Li^(+) transport, thus achieving a high ion conductivity of 0.102 m S cm^(-1)at 80 °C and a high lithium-ion transference number of 0.855 at room temperature. According to density functional theory(DFT)calculations, Li-ion migration mainly adopted in-plane transport rather than the axial pathway, which may be due to the shorter hopping distances in the planar pathway. The results suggest an effective strategy for the design and development of all-solidstate ionic conductors for achieving high-performance LIBs.

关键词： lithium ion batteries(LIBs) covalent organic frameworks(COFs) solid-state ion conductors solid-state electrolytes ion conductivity

Implementation of Teacher Training in China and Its Policy Implications

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China & World Economy 2016年第3期24卷 86-104页

作者： Hongyan liu chengfang liu Fang Chang Prashant Loyalka PhD candidate Center for Experimental Economics in Education Shaanxi Normal University China. Associate Professor School of Advanced Agricultural Sciences Peking University China. Assistant Professor Center for Experimental Economics in Education Shaanxi Normal University China. Associate Professor Freeman Spogli Institute for International Studies Stanford University USA.

This study describes the current teacher training system in China, including the prevalence of teacher training, the types of training, training content and the ways that training is delivered. The paper presents subjective evaluations of training for principaIs and teachers using four diverse datasets. The results show that the National Teacher Training Project OVTTP） deviates from official policy objectives in several respects. The subjects of training programs and training content are not fully compliant with policy objectives. In addition, training opportunities are offered to a smaller proportion of rural teachers than urban teachers. It is found that the proportion of teachers and principals satisfied with the NTTP is lower than that for other types of training. Therefore, measures should be taken to increase training opportunities for rural teachers and to ensure the quality of training for all teachers.

关键词： China program implementation teacher training

Single-Component Color-Tunable Smart Organic Emitters with Simultaneous Multistage Stimuli-Responsiveness and Multimode Emissions

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Research 2024年第2期2023卷 719-728页

作者： Yu Yan chengfang liu Jianzhong Fan Yusheng Li Huanling liu Qian Wang Xiangchun Lil Junfeng Li Wen-Yong Lai State Key Laboratory of Organic Electronics and Information Displays(SKLOEID) Institute of Advanced Materials(IAM)School of Chemistry and Life SciencesNanjing University of Posts&Telecommunications9 Wenyuan RoadNanjng 210023China Shandong Province Key Laboratory of Medical Physics and Image Processing Technology School of Physics and ElectronicsShandong Normal UniversityJinan 250358China

Achieving color-tunable emission in single-component organic emitters with multistage stimuli-responsiveness is of vital significance for intelligent optoelectronic applications,but remains enormously ***,we present an unprecedented example of a color-tunable single-component smart organic emitter(DDOP)that simultaneously exhibits multistage stimuli-responsiveness and multimode *** based on a highly twisted amide-bridged donor-tcceptor-donor structure has been found to facilitate intersystem crossing,form multimode emissions,and generate multiple emissive species with multistage *** pristine crystalline powders exhibit abnormal excitation-dependent emissions from a monomer-dominated blue emission centered at 470 nm to a dimer-dominated yellow emission centered at 550 nm through decreasing the ultraviolet(UV)excitation wavelengths,whereas DDOP single crystals show a wide emission band with a main emission peak at 585 nm when excited at different *** emission behaviors of pristine crystalline powders and single crystals are different,demonstrating emission features that are closely related to the aggregation *** work has developed color-tunable single-component organic emitters with simultaneous multistage stimuli-responsiveness and multimode emissions,which is vital for expanding intelligent optoelectronic applications,including multilevel information encryption,multicolor emissive patterns,and visual monitoring of UV wavelengths.

关键词： donor excitation Smart

Wavelength-tunable organic semiconductor lasers based on elastic distributed feedback gratings

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Journal of Semiconductors 2023年第3期44卷 68-75页

作者： chengfang liu He Lin Dongzhou Ji Qun Yu Shuoguo Chen Ziming Guo Qian Luo Xu liu Wenyong Lai State Key Laboratory for Organic Electronics and Information Displays(SKLOEID) Institute of Advanced Materials(IAM)Nanjing University of Posts&TelecommunicationsNanjing 210023China

Wavelength-tunable organic semiconductor lasers based on mechanically stretchable polydimethylsiloxane (PDMS) gratings were developed. The intrinsic stretchability of PDMS was explored to modulate the period of the distributed feedback gratings for fine tuning the lasing wavelength. Notably, elastic lasers based on three typical light-emitting molecules show com-parable lasing threshold values analogous to rigid devices and a continuous wavelength tunability of about 10 nm by mechanic-al stretching. In addition, the stretchability provides a simple solution for dynamically tuning the lasing wavelength in a spec-tral range that is challenging to achieve for inorganic counterparts. Our work has provided a simple and efficient method of fab-ricating tunable organic lasers that depend on stretchable distributed feedback gratings, demonstrating a significant step in the advancement of flexible organic optoelectronic devices.

关键词： stretchable electronics organic semiconductor lasers elastic lasers distributed feedback(DFB)gratings wavelength tunability

How Off-farm Employment Affects Technical Efficiency of China＇s Farms＂ The Case of Jiangsu

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China & World Economy 2016年第3期24卷 37-51页

作者： Linxiu Zhang Weiliang Su Tor Eriksson chengfang liu Professor Center for Chinese Agricultural Policy Institute of Geographic Sciences and Natural Resources Research Chinese Academy of Sciences China PhD candidate Center for Chinese Agricultural Policy Institute of Geographic Sciences and Natm'al Resources Research Chinese Academy of Sciences Sino-Danish Center for Education and Research University of Chinese Academy of Sciences China Professor Department of Economics and Business Economics Aarhus University Denmark. Associate Professor School of Advanced Agricultural Sciences Peking University China

Using three-wave survey data for four villages of Jiangsu Province in China, the present paper examines whether and to what extent off-farm employment affects the technical efficiency of agricultural production. The level of technical efficiency is measured using a stochastic frontier production function approach. Based on estimation results from instrumental variable panel quantile regressions we find that there is a positive significant effect of off-farm employment on the level of farm technical efficiency. We also find that fragmentation of farmland is a barrier to the improvement of technical efficiency. In addition, we find a downward trend in the level of agricultural technical efficiency among our sample. Therefore, the Chinese Government should stimulate agricultural mechanization and the development of farming techniques to improve technical efficiency in the context of increasing off-farm employment.

关键词： off-farm employment stochastic frontier analysis technical efficiency

Effect of Migration on Children's Self-esteem in Rural China

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China & World Economy 2014年第4期22卷 83-101页

作者： Xuefeng Zhan Shaoping Li chengfang liu Linxiu Zhang Institute of Geographic Sciences and Natural Resources Research Chinese Academy of Sciences University of Chinese Academy of Sciences Center for Chinese Agricultural Policy Institute of Geographical Sciences and Natural Resource ResearchChinese Academy of Sciences

China＇s rapid economic growth has been facilitated by its large volume of rural to urban migration. China ＇s projected future development, especially increasing urbanization, implies that such migration will further intensify. However, migration does not come without cost. There are concerns about the potential negative impacts of migration on children＇s care, education, and, in particular, the self-esteem of children left behind in villages where one or both parents have out-migrated to cities. In this paper, we employ unique survey data collected from Shaanxi Province, where more than 4700 ninth grade students from 36 rural junior high schools in five counties were surveyed in late 2011. The results show that having both parents migrate into cities significantly reduced children ＂s self-esteem. The effects are also gender sensitive. Girls that had a father or both parents who had out-migrated were inclined to have lower self-esteem than boys. Moreover, our study findings indicate that parental migration decreased children ＂s self-esteem more for individuals with initial low self-esteem.

关键词： Key words: children left-behind migration rural China self-esteem

China's Labor Transition and the Future of China's Rural Wages and Employment

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China & World Economy 2013年第3期21卷 4-24页

作者： Qiang Li Jikun Huang Renfu Luo chengfang liu Beijing Forestry University Center for Chinese Agricultural Policy Institute of Geographical Sciences and Natural Resources ResearchChinese Academy of Sciences

This paper contributes to the assessment of China＇s rural labor markets. According to our data, the increase in off-farm employment that China experienced during the 1980s and 1990s continued during the 2000s. Our analysis shows that migration has become the most prevalent off-farm activity, although the destination of migrants is shifting from outside of one＇s province to destinations closer to home. The present paperfinds that large shares of male and female individuals, especially those under 40 years, are working off the farm. These findings represent an important contribution to the labor economics field. First, the results of the present paper reveal that the labor transition from the agricultural sector to the non-agricultural sector for key segments of China＇s rural labor force is nearly complete. Second, although a large share of China ＂s rural labor force work in agriculture, most of these workers are older men and women （and likely would not be willing to take low-wage, labor-intensive jobs）. Third, the rising unskilled wage rate in China is partially a result of the tightening of the labor force in the young age cohorts. Finally, due to factors associated with the one child policy and other demographic transition forces, successive age cohorts will continue to fall in absolute number in the coming decade. Assuming China＇s growth continues, we expect to see further wage increases since it will take higher wages to coax more workers to work off the farm.

关键词： China labor force participation rural wages

White Electroluminescence with Simultaneous Three-Color Emission from a Four-Armed Star-Shaped Single-Polymer System

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Chinese Journal of Chemistry 2015年第8期33卷 873-880页

作者： Yuanda Jiu Jianyun Wang chengfang liu Wenyong Lai Lingling Zhao Xiangchun Li Yi Jiang Weidong Xu Xinwen Zhang Wei Huang Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials Jiangsu National Synergetic Innovation Center for Advanced Materials Nanjing University of Posts & Telecommunications Nanjing Jiangsu 210023 China Key Laboratory of Flexible Electronics & Institute of Advanced Materials Jiangsu National Synergetie innovation Center for Advanced Materials Nanjing Tech University Nanjing Jiangsu 211816 China

A four-armed star-shaped single-polymer system with 4,7-bis（5-（4-（9H-carbazol-9-yl）phenyl）-4-hexylthio- phen-2-yl）benzo[c][1,2,5]thiadiazole （FTBT） as a red emissive core, polyfluorene （PF） as blue emissive arms and 1,3-benzo thiadiazole （BT） as green emissive dopants was designed and synthesized, in which red, green, and blue （RGB） emission balance can be achieved by adjusting the doping concentration of FTBT and BT discreetly. A typ- ical single-emissive-layer device （ITO/PEDOT：PSS/polymer/TPBI/LiF/Al） was studied and discussed, realizing a pure and stable white emission with a luminous efficiency （LE） of 1.59 cd·A^-1 and CIE coordinates of （0.31, 0.34）. The high-color-quality white electroluminescence of the devices could be mainly attributed to the suppressed in- termolecular interactions, and partial energy transfer from the blue PF arms to the red and green dopants.

关键词： white electroluminescence hyperbranched polymers multi-armed structures Forster resonance energy transfer organic light-emitting diodes

How Are Secondary Vocational Schools in China Measuring up to Government Benchmarks?

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China & World Economy 2013年第3期21卷 98-120页

作者： Hongmei Yi Linxiu Zhang chengfang liu James Chu Prashant Loyalka May Maani Jianguo Wei Center for Chinese Agricultural Policy Institute for Geographical Sciences and Natural Resource ResearchChinese Academy of Sciences Rural Education Action Project Freeman Spogli Institute for International StudiesStanford University Freeman Spogli Institute for International Studies Stanford University China Institute for Educational Finance Research Peking University

Drawing on a survey of106 secondary vocational schools and 7309 students in two provinces of China, this descriptive paper assesses whether vocational schooling is measuring up to government benchmarks for quality and whether poor students are able to access quality schools. We find that secondary vocational schools have met government benchmarks for teacher qualification and training, student opportunities forpractical training and adequate facilities. Furthermore, poor students access schools of similar quality to non-poor students, even though 34percent of poor students do not receive financial aid. We conclude that recent policies are successfully ensuring secondary vocational school quality and equity of access to school quality between poor and non-poor students. However, financial aid policies should be re-examined, such that poor students receive sufficient coverage. Moreover, given that input-based measures only proxy school quality, the government should consider holding schools accountable for outcomes such as student learning.

关键词： access China financial aid quality secondary vocational school