The global COVID-19 pandemic caused various economic contraction in most countries,including all of China’s major trading partners.Using a difference-in-differences model,this study examines the impact of the COVID-1...The global COVID-19 pandemic caused various economic contraction in most countries,including all of China’s major trading partners.Using a difference-in-differences model,this study examines the impact of the COVID-19 pandemic on China’s monthly exports from January 2019 to May 2020.We find strong and robust evidence that China’s exports to countries at high risk from the pandemic experienced a larger decline than exports to low-risk countries after the onset of the pandemic,with the prices of exports increasing significantly.Furthermore,the results of a triple differences model show heterogeneous effects across different industries and goods.Chinese industries located upstream in the global value chain are more vulnerable than those located downstream.Industries with high labor and contract intensity(proxies for processing trade)experienced greater declines than other industries.Exports of goods with high import elasticity of substitution experienced higher prices and moderate volume losses due to the pandemic.展开更多
In recent years, due to the rapid development of high-performance small molecule acceptor (SMA) materials, the researches on p-type electron donor materials for matching with current efficient SMAs have become importa...In recent years, due to the rapid development of high-performance small molecule acceptor (SMA) materials, the researches on p-type electron donor materials for matching with current efficient SMAs have become important. By means of asymmetric strategies to optimize the energy levels and inter/intramolecular interactions of molecules, we designed and synthesized an asymmetric aromatic side chain quinoxaline-based polymer donor TPQ-0F. Meanwhile, we took advantage of F atom which could form noncovalent interaction and strong electron-withdrawing property, to obtain the optimized quinoxaline-based polymer donors TPQ-1F, TPQ-1Fi and TPQ-2F. Eventually, the binary device based on TPQ-2F achieved an efficient power conversion efficiency (PCE) of 16.27%, which attributed to balanced hole/electron mobilities, less charge carrier recombination, and more favorable aggregation morphology. Our work demonstrates the great potential of asymmetric aromatic side chain quinoxaline-based polymer donors on optimizing the morphology of blending films, improving inter/intramolecular interactions, and subtly tuning energy level, finally for more efficient organic solar cells.展开更多
Since 2020,the Modi government has sought to implement the policy of industrial substitution for China as an important approach to economic autonomy and industrial rejuvenation.Based on the Modi government’s industri...Since 2020,the Modi government has sought to implement the policy of industrial substitution for China as an important approach to economic autonomy and industrial rejuvenation.Based on the Modi government’s industrial policy practices,its substitution policy for Chinese industries comprises three parts.A favorable domestic political ecology,an encouraging geostrategic environment,and a relatively solid industrial foundation provide the Modi government with the conditions and confidence to implement this policy.Nevertheless,owing to the conservatism of India’s domestic political culture,expediency in helping and appeasing India by the US,reversal of economic globalization,and sustainability of China’s industrial policy to break new ground,Modi’s substitution policy for Chinese industries has found limited success.However,considering India’s substantial economic size and the strategic support of the US and other developed nations in the West,the Modi government’s substitution policy for Chinese industries can still disrupt China’s efforts to build and maintain a healthier production chain.展开更多
Three types of semi-cry stalline photovoltaic polymers were synthesized by incorporating a siloxane-terminated organic/inorganic hybrid side-chain and changing the number of fluorine substituents.A branch point away f...Three types of semi-cry stalline photovoltaic polymers were synthesized by incorporating a siloxane-terminated organic/inorganic hybrid side-chain and changing the number of fluorine substituents.A branch point away from a polymer main backbone in the siloxane-containing side-chains and the intra-and/or interchain noncovalent coulombic interactions enhance a chain planarity and facile interchain organization.The resulting polymers formed strongly agglomerated films with high roughness,suggesting strong intermolecular interactions.The optical band gap of ca.1.7 eV was measured for all polymers with a pronounced shoulder peak due to tight π-π stacking.With increasing the fluorine substituents,the frontier energy levels decreased and preferential face-on orientation was observed.The siloxane-terminated side-chains and fluorine substitution promoted the intermolecular packing,showing well resolved lamellar scatterings up to(300) for this series of polymers in the grazing incidence wide angle X-ray scattering measurements.The PPsiDTBT,PPsiDTFBT and PPsiDT2 FBT devices showed a power conversion efficiency of 3.16%,4.40%and 5.65%,respectively,by blending with PC_(71)BM.Langevin-type bimolecular charge recombination was similar for three polymeric solar cells.The main loss in the photocurrent generation for PPsiDTBT:PC_(71)BM was interpreted to originate from the trap assisted charge recombination by measuring light-intensity dependent short-circuit current density(J_(SC)) and open-circuit voltage(V_(Oc)).Our results provide a new insight into the rational selection of solubilizing substituents for optimizing crystalline interchain packing with appropriate miscibility with PC71 BM for further optimizing polymer solar cells.展开更多
Short chain chlorinated paraffins （SCCPs） are not only research focus of environmental issues but also interesting model mol- ecules for organic chemistry which exhibit diverse conformation preference and intramolec...Short chain chlorinated paraffins （SCCPs） are not only research focus of environmental issues but also interesting model mol- ecules for organic chemistry which exhibit diverse conformation preference and intramolecular noncovalent interactions （NCIs）. A systematic study was conducted to reveal the conlk）rmation preference and the related intramolecular NCIs in two C^-isomers of SCCPs, 5,5,6,6-tetrachlorodecane and 4,4,6,6-1etrachlorodecane. The overall conformation profile was deter- mined on the basis of relative energies calculated at the MP2/6-311＋＋G（d,p） level with the geometries optimized by B3LYP/6-31 l＋＋G（d,p） method. Then, quantum theory of atoms in molecules （QTAIM） has been adopted to identify the NCls in the selected conformers of the model molecules at both B31~YP/6-31 l＋＋G（d,p） and M06-2X/aug-cc-pvdz level. Different chlorine substitution modes result in varied conformation preference. No obvious gauche effect can be observed tk）r the SCCPs with chlorination on adjacent carbon atoms. The most stable conformer of 5,5,6,6-tetrachlorodecane （tTt） has its three dihedral angles in the T configuration, and there is no intramolecular N（3s found in this molecule. On the contrary, the chlorination on interval carbon atoms favors the adoption of gauche configmation for the H C C CI axis. Not only inlramolecular H-..CI contacts but also H---H interactions have been identified as driving forces to compensate the instability from steric crowding ot the gauche configuration. The gggg and g＇g＇g＇g＇ conformers are the most popular ones, while the populations of tggg and tg＇g＇g＇ conformer are second to those of the gggg and g＇g＇g＇g＇ conformers. Meanwhile, the M06-2X method with large basis sets is preferred for identification of subtle intramolecular NCIs in large molecules like SCCPs.展开更多
文摘The global COVID-19 pandemic caused various economic contraction in most countries,including all of China’s major trading partners.Using a difference-in-differences model,this study examines the impact of the COVID-19 pandemic on China’s monthly exports from January 2019 to May 2020.We find strong and robust evidence that China’s exports to countries at high risk from the pandemic experienced a larger decline than exports to low-risk countries after the onset of the pandemic,with the prices of exports increasing significantly.Furthermore,the results of a triple differences model show heterogeneous effects across different industries and goods.Chinese industries located upstream in the global value chain are more vulnerable than those located downstream.Industries with high labor and contract intensity(proxies for processing trade)experienced greater declines than other industries.Exports of goods with high import elasticity of substitution experienced higher prices and moderate volume losses due to the pandemic.
基金supported by the National Natural Science Foundation of China(Nos.21875286 and 52125306,)J.Yuan acknowledges the National Natural Science Foundation of China(No.22005347)+2 种基金the Natural Science Foundation of Hunan Province(No.2021JJ20068)L.Jiang acknowledges the Open Sharing Fund for the Large-scale Instruments and Equipments of Central South University(No.CSUZC202218)the Natural Science Foundation of Hunan Province(No.2021JJ30793).
文摘In recent years, due to the rapid development of high-performance small molecule acceptor (SMA) materials, the researches on p-type electron donor materials for matching with current efficient SMAs have become important. By means of asymmetric strategies to optimize the energy levels and inter/intramolecular interactions of molecules, we designed and synthesized an asymmetric aromatic side chain quinoxaline-based polymer donor TPQ-0F. Meanwhile, we took advantage of F atom which could form noncovalent interaction and strong electron-withdrawing property, to obtain the optimized quinoxaline-based polymer donors TPQ-1F, TPQ-1Fi and TPQ-2F. Eventually, the binary device based on TPQ-2F achieved an efficient power conversion efficiency (PCE) of 16.27%, which attributed to balanced hole/electron mobilities, less charge carrier recombination, and more favorable aggregation morphology. Our work demonstrates the great potential of asymmetric aromatic side chain quinoxaline-based polymer donors on optimizing the morphology of blending films, improving inter/intramolecular interactions, and subtly tuning energy level, finally for more efficient organic solar cells.
文摘Since 2020,the Modi government has sought to implement the policy of industrial substitution for China as an important approach to economic autonomy and industrial rejuvenation.Based on the Modi government’s industrial policy practices,its substitution policy for Chinese industries comprises three parts.A favorable domestic political ecology,an encouraging geostrategic environment,and a relatively solid industrial foundation provide the Modi government with the conditions and confidence to implement this policy.Nevertheless,owing to the conservatism of India’s domestic political culture,expediency in helping and appeasing India by the US,reversal of economic globalization,and sustainability of China’s industrial policy to break new ground,Modi’s substitution policy for Chinese industries has found limited success.However,considering India’s substantial economic size and the strategic support of the US and other developed nations in the West,the Modi government’s substitution policy for Chinese industries can still disrupt China’s efforts to build and maintain a healthier production chain.
基金supported by the National Research Foundation of Korea 2015R1A2A1A15055605,2015M1A2A2057506,2015R1D1A1A09056905,2016M1A2A2940911)
文摘Three types of semi-cry stalline photovoltaic polymers were synthesized by incorporating a siloxane-terminated organic/inorganic hybrid side-chain and changing the number of fluorine substituents.A branch point away from a polymer main backbone in the siloxane-containing side-chains and the intra-and/or interchain noncovalent coulombic interactions enhance a chain planarity and facile interchain organization.The resulting polymers formed strongly agglomerated films with high roughness,suggesting strong intermolecular interactions.The optical band gap of ca.1.7 eV was measured for all polymers with a pronounced shoulder peak due to tight π-π stacking.With increasing the fluorine substituents,the frontier energy levels decreased and preferential face-on orientation was observed.The siloxane-terminated side-chains and fluorine substitution promoted the intermolecular packing,showing well resolved lamellar scatterings up to(300) for this series of polymers in the grazing incidence wide angle X-ray scattering measurements.The PPsiDTBT,PPsiDTFBT and PPsiDT2 FBT devices showed a power conversion efficiency of 3.16%,4.40%and 5.65%,respectively,by blending with PC_(71)BM.Langevin-type bimolecular charge recombination was similar for three polymeric solar cells.The main loss in the photocurrent generation for PPsiDTBT:PC_(71)BM was interpreted to originate from the trap assisted charge recombination by measuring light-intensity dependent short-circuit current density(J_(SC)) and open-circuit voltage(V_(Oc)).Our results provide a new insight into the rational selection of solubilizing substituents for optimizing crystalline interchain packing with appropriate miscibility with PC71 BM for further optimizing polymer solar cells.
基金the Chinese Academy of Sciences (KZCX2-YW-BR-25, XDB14030500, YSW2013B01)the National High Technology Research and Development Program of China (2013AA065201)
文摘Short chain chlorinated paraffins （SCCPs） are not only research focus of environmental issues but also interesting model mol- ecules for organic chemistry which exhibit diverse conformation preference and intramolecular noncovalent interactions （NCIs）. A systematic study was conducted to reveal the conlk）rmation preference and the related intramolecular NCIs in two C^-isomers of SCCPs, 5,5,6,6-tetrachlorodecane and 4,4,6,6-1etrachlorodecane. The overall conformation profile was deter- mined on the basis of relative energies calculated at the MP2/6-311＋＋G（d,p） level with the geometries optimized by B3LYP/6-31 l＋＋G（d,p） method. Then, quantum theory of atoms in molecules （QTAIM） has been adopted to identify the NCls in the selected conformers of the model molecules at both B31~YP/6-31 l＋＋G（d,p） and M06-2X/aug-cc-pvdz level. Different chlorine substitution modes result in varied conformation preference. No obvious gauche effect can be observed tk）r the SCCPs with chlorination on adjacent carbon atoms. The most stable conformer of 5,5,6,6-tetrachlorodecane （tTt） has its three dihedral angles in the T configuration, and there is no intramolecular N（3s found in this molecule. On the contrary, the chlorination on interval carbon atoms favors the adoption of gauche configmation for the H C C CI axis. Not only inlramolecular H-..CI contacts but also H---H interactions have been identified as driving forces to compensate the instability from steric crowding ot the gauche configuration. The gggg and g＇g＇g＇g＇ conformers are the most popular ones, while the populations of tggg and tg＇g＇g＇ conformer are second to those of the gggg and g＇g＇g＇g＇ conformers. Meanwhile, the M06-2X method with large basis sets is preferred for identification of subtle intramolecular NCIs in large molecules like SCCPs.
