The core sample from well QZ-4 is an important climate archive for the central Tibetan Plateau in the middle-late Pleistocene. In this work, a detailed pollen analysis of it is carried out to provide a preliminary ins...The core sample from well QZ-4 is an important climate archive for the central Tibetan Plateau in the middle-late Pleistocene. In this work, a detailed pollen analysis of it is carried out to provide a preliminary insight into the paleo-climate and paleo-altimetry change in the central Tibetan Plateau. It can be concluded that the pollen assemblage can be obviously divided into two pollen zones, Pollen zone I (251.1 - 314 m in depth, 120.0 - 345.8 ka BP.) and Pollen zone II (200 - 251.1 m in depth, 105.4 - 120 ka BP.). The paleo-climate during pollen zone I deposition period was comparatively colder and wetter than it during the pollen zone II deposition period. After Gonghe Movement, the center of Tibetan Plateau was uplifted about 300 m (from 3500 - 3700 m to 3800 - 4000 m in elevation). The wind was changed from horizontal or downward direction to upward direction, in the study area. In the central of Tibetan Plateau, the climate change seems to be mainly driven by global climate change, and that tectonic uplift may have been a subordinate influence at the middle-late Pleistocene.展开更多
As the Reynolds number increases, the skin friction has been identified as the dominant drag in many practical applications. In the present paper, the effects of the Reynolds number on the mean skin friction decomposi...As the Reynolds number increases, the skin friction has been identified as the dominant drag in many practical applications. In the present paper, the effects of the Reynolds number on the mean skin friction decomposition in turbulent channel flows up to Reτ= 5 200 are investigated based on two different methods, i.e., the FukagataIwamoto-Kasagi(FIK) identity(FUKAGATA, K., IWAMOTO, K., and KASAGI, N.Contribution of Reynolds stress distribution to the skin friction in wall-bounded flows.Physics of Fluids, 14(11), L73–L76(2002)) and the Renard-Deck(RD) identity(DECK,S., RENARD, N., LARAUFIE, R., and WEISS, P.′E. Large-scale contribution to mean wall shear stress in high-Reynolds-number flat-plate boundary layers up to Reθ= 13 650.Journal of Fluid Mechanics, 743, 202–248(2014)). The direct numerical simulation(DNS) data provided by Lee and Moser(LEE, M. and MOSER, R. D. Direct numerical simulation of turbulent channel flow up to Reτ≈ 5 200. Journal of Fluid Mechanics,774, 395–415(2015)) are used. For these two skin friction decomposition methods, their decomposed constituents are discussed and compared for different Reynolds numbers.The integrands of the decomposed constituents are locally analyzed across the boundary layer to assess the actions associated with the inhomogeneity and multi-scale nature of turbulent motion. The scaling of the decomposed constituents and their integrands are presented. In addition, the boundary layer is divided into three sub-regions to evaluate the contributive proportion of each sub-region with an increase in the Reynolds number.展开更多
Direct numerical simulations (DNS) of turbulent flow over a drag-reducing and a drag-increasing riblet configuration are performed. Three-dimensional two-point statistics are presented for the first time to quantify t...Direct numerical simulations (DNS) of turbulent flow over a drag-reducing and a drag-increasing riblet configuration are performed. Three-dimensional two-point statistics are presented for the first time to quantify the interaction of the riblet surfaces with the coherent, energy-bearing eddy structures in the near-wall region. Results provide statistical evidence that the averaged organization of the streamwise vortices in the drag-reducing case is lifted above the riblet tip, while in the drag-increasing case the streamwise vortices are embedded further into the riblet cove. In the spanwise direction, the cores of the streamwise vortices over the riblet surfaces are shown to be closer to each other than those for flow over the smooth wall, and wider riblet spacing leads to more reduction on their spanwise distances. In the cases with riblets the streamwise vortices have longer streamwise lengths, but their inclination angles do not change much.展开更多
In this paper,we have developed a decarboxylative amination of carboxylic acids with nitroarenes for the synthesis of secondary amines.The protocol is performed at mild conditions without the use of noble metals as ca...In this paper,we have developed a decarboxylative amination of carboxylic acids with nitroarenes for the synthesis of secondary amines.The protocol is performed at mild conditions without the use of noble metals as catalysts.A wide range of structurally diverse secondary amines could be obtained in good yields(up to 94%)with good functional group tolerance.This transformation shows good to excellent selectivity,avoiding the generation of over alkylated byproducts.展开更多
The electro-optical payloads on mobile platforms generally suffer undesirable vibrations generated by maneuvers and turbulence.These vibrations are in six degrees of freedom and cause line-of-sight jitters,resulting i...The electro-optical payloads on mobile platforms generally suffer undesirable vibrations generated by maneuvers and turbulence.These vibrations are in six degrees of freedom and cause line-of-sight jitters,resulting in image blurring and loss of tracking accuracy.In this paper,a Hexapod Vibration Isolation System(HVIS)is proposed and optimized to solve this problem.The optimization aims to centralize and minimize the natural frequencies of HVIS,for expanding the vibration isolation bandwidth and improving the vibration isolation in the higher frequency band.Considering that the design space for HVIS is limited and interfered with the frames of the mobile platform,a non-collision algorithm is proposed and applied in the optimization to obtain the feasible optimal design.The optimization result shows that the natural frequency bandwidth has been reduced by 42.9%,and the maximum natural frequency is reduced by 30.2%.The prototypes of initial and optimal designs are manufactured and tested.Both simulated and experimental results demonstrate the validity of the optimization,and the optimal design provides a maximum of 15 dB more isolation in rotation direction than the initial design.展开更多
We report an unprecedented C-H bond functionalization of cyclopropenes enabled by dinuclear gold catalysis.Highly selective C-H allylation,alkynylation and halogenation of cyclopropenes with organic halides have been ...We report an unprecedented C-H bond functionalization of cyclopropenes enabled by dinuclear gold catalysis.Highly selective C-H allylation,alkynylation and halogenation of cyclopropenes with organic halides have been realized.The reaction does not require strong external oxidants and affords access to functionalized cyclopropenes in moderate to good yields.The reductive elimination process to controllably construct C-C or C-X bonds can be tuned by using different dinuclear gold catalysts.展开更多
Ketones serve as one of the most critical building blocks in organic synthesis,involving numerous functional group transformations.Herein,we rep ort an unprecedented photoredox-nickel metallap hotoredox-catalyzed deca...Ketones serve as one of the most critical building blocks in organic synthesis,involving numerous functional group transformations.Herein,we rep ort an unprecedented photoredox-nickel metallap hotoredox-catalyzed decarboxylative acylation of common aliphatic acids with readily available aromatic and aliphatic thioesters.A wide range of structurally diverse asymmetrical aryl alkyl and dialkyl ketones have been constructed in yields of up to 98% with this strategy.The protocol has excellent reaction selectivity and functional group compatibility,representing a significant step forward in ketone synthesis.The one-pot decarboxylative acylation at the gram scale from two different carboxylic acids and the late-stage application for the synthesis of complex ketones shows its synthetic robustness.Both mechanistic experiments and density functional theory(DFT)calculations suggest that the decarboxylative acylation reaction operates via an underdeveloped Ni(Ⅰ)-Ni(Ⅱ)-Ni(Ⅰ)-Ni(Ⅲ)-Ni(Ⅰ)catalytic cycle.展开更多
As a key component of electro-optical systems, a Two-axis Scan mirror AssemblY(TSAY) is usually used for Line-of-Sight(LOS) precision pointing, tracking, scanning, and stabilizing. Therefore, it is necessary for a TSA...As a key component of electro-optical systems, a Two-axis Scan mirror AssemblY(TSAY) is usually used for Line-of-Sight(LOS) precision pointing, tracking, scanning, and stabilizing. Therefore, it is necessary for a TSAY to have a large angular range, high dynamic characteristics, and small mirror surface distortion. Furthermore, vibration from carriers of electro-optical systems, such as spacecraft and airplanes, is inevitable, so it is critical to guarantee the control accuracy of a TSAY under vibration. In this paper, a TSAY prototype is designed and developed. To increase the control bandwidth, structural topology optimization is applied to the TSAY’s elliptical mirror to reduce the moment of inertia, meanwhile keeping surface flatness. A flexible hinge is adopted to achieve a large angular range. To suppress the angular perturbation caused by the base linear vibration, an adaptive feedforward loop with base-integrated Micro-Electro-Mechanical System(MEMS) accelerators is constructed to enhance the TSAY’s feedback loop. Simulation and experimental results show that the TSAY prototype’s two-axis mechanical angular ranges are more than ±3.2°, the mirror surface flatness Root Mean Square(RMS) value is better than 0.04 k, and the closed-loop bandwidth is beyond 330 Hz. These are suitable for most applications. Besides, the angular perturbation caused by the base vibration can be suppressed more than 37.7% with the addition of the adaptive feedforward loop.展开更多
文摘The core sample from well QZ-4 is an important climate archive for the central Tibetan Plateau in the middle-late Pleistocene. In this work, a detailed pollen analysis of it is carried out to provide a preliminary insight into the paleo-climate and paleo-altimetry change in the central Tibetan Plateau. It can be concluded that the pollen assemblage can be obviously divided into two pollen zones, Pollen zone I (251.1 - 314 m in depth, 120.0 - 345.8 ka BP.) and Pollen zone II (200 - 251.1 m in depth, 105.4 - 120 ka BP.). The paleo-climate during pollen zone I deposition period was comparatively colder and wetter than it during the pollen zone II deposition period. After Gonghe Movement, the center of Tibetan Plateau was uplifted about 300 m (from 3500 - 3700 m to 3800 - 4000 m in elevation). The wind was changed from horizontal or downward direction to upward direction, in the study area. In the central of Tibetan Plateau, the climate change seems to be mainly driven by global climate change, and that tectonic uplift may have been a subordinate influence at the middle-late Pleistocene.
基金国家重点研发项目(2022YFA1503200,2021YFC2101901)国家自然科学基金(22122103,21971108,21971111,22271144)+1 种基金中央高校基本科研业务费(020514380304,020514380252 and 020514380272)江苏省研究生科研与实践创新计划项目(KYCX22_0100).
基金Project supported by the National Basic Research Program of China(973 Program)(No.2014CB744802)the National Natural Science Foundation of China(No.11772194)
文摘As the Reynolds number increases, the skin friction has been identified as the dominant drag in many practical applications. In the present paper, the effects of the Reynolds number on the mean skin friction decomposition in turbulent channel flows up to Reτ= 5 200 are investigated based on two different methods, i.e., the FukagataIwamoto-Kasagi(FIK) identity(FUKAGATA, K., IWAMOTO, K., and KASAGI, N.Contribution of Reynolds stress distribution to the skin friction in wall-bounded flows.Physics of Fluids, 14(11), L73–L76(2002)) and the Renard-Deck(RD) identity(DECK,S., RENARD, N., LARAUFIE, R., and WEISS, P.′E. Large-scale contribution to mean wall shear stress in high-Reynolds-number flat-plate boundary layers up to Reθ= 13 650.Journal of Fluid Mechanics, 743, 202–248(2014)). The direct numerical simulation(DNS) data provided by Lee and Moser(LEE, M. and MOSER, R. D. Direct numerical simulation of turbulent channel flow up to Reτ≈ 5 200. Journal of Fluid Mechanics,774, 395–415(2015)) are used. For these two skin friction decomposition methods, their decomposed constituents are discussed and compared for different Reynolds numbers.The integrands of the decomposed constituents are locally analyzed across the boundary layer to assess the actions associated with the inhomogeneity and multi-scale nature of turbulent motion. The scaling of the decomposed constituents and their integrands are presented. In addition, the boundary layer is divided into three sub-regions to evaluate the contributive proportion of each sub-region with an increase in the Reynolds number.
基金the National Basic Research Program of China (973 program)(Grants 2014CB744802 and 2014CB744804)the National Natural Science Foundation of China (Grants 11772194 and 91441205).
文摘Direct numerical simulations (DNS) of turbulent flow over a drag-reducing and a drag-increasing riblet configuration are performed. Three-dimensional two-point statistics are presented for the first time to quantify the interaction of the riblet surfaces with the coherent, energy-bearing eddy structures in the near-wall region. Results provide statistical evidence that the averaged organization of the streamwise vortices in the drag-reducing case is lifted above the riblet tip, while in the drag-increasing case the streamwise vortices are embedded further into the riblet cove. In the spanwise direction, the cores of the streamwise vortices over the riblet surfaces are shown to be closer to each other than those for flow over the smooth wall, and wider riblet spacing leads to more reduction on their spanwise distances. In the cases with riblets the streamwise vortices have longer streamwise lengths, but their inclination angles do not change much.
基金National Key Research and Development Program of China(2022YFA1503200,2021YFC2101901)the National Natural Science Foundation of China(22122103,22101130,22001117,21971108,22271144)Fundamental Research Funds for the Central Universities(020514380304,020514380252,020514380272)for financial support.
文摘In this paper,we have developed a decarboxylative amination of carboxylic acids with nitroarenes for the synthesis of secondary amines.The protocol is performed at mild conditions without the use of noble metals as catalysts.A wide range of structurally diverse secondary amines could be obtained in good yields(up to 94%)with good functional group tolerance.This transformation shows good to excellent selectivity,avoiding the generation of over alkylated byproducts.
基金supported by the National Key R&D Program of China(No.2021YFA1003503)。
文摘The electro-optical payloads on mobile platforms generally suffer undesirable vibrations generated by maneuvers and turbulence.These vibrations are in six degrees of freedom and cause line-of-sight jitters,resulting in image blurring and loss of tracking accuracy.In this paper,a Hexapod Vibration Isolation System(HVIS)is proposed and optimized to solve this problem.The optimization aims to centralize and minimize the natural frequencies of HVIS,for expanding the vibration isolation bandwidth and improving the vibration isolation in the higher frequency band.Considering that the design space for HVIS is limited and interfered with the frames of the mobile platform,a non-collision algorithm is proposed and applied in the optimization to obtain the feasible optimal design.The optimization result shows that the natural frequency bandwidth has been reduced by 42.9%,and the maximum natural frequency is reduced by 30.2%.The prototypes of initial and optimal designs are manufactured and tested.Both simulated and experimental results demonstrate the validity of the optimization,and the optimal design provides a maximum of 15 dB more isolation in rotation direction than the initial design.
基金supported by the National Natural Science Foundation of China(22001116,22001117,21971111,21971108,21732003)the Natural Science Foundation of Jiangsu Province(BK20190006,BK20190285)+3 种基金the Fundamental Research Funds for the Central Universities(020514380252)the“Innovation&Entrepreneurship Talents Plan”of Jiangsu Provincethe Guangdong Basic and Applied Basic Research Foundation(2020A1515110816)the Foundation of Advanced Catalytic Engineering Research Center of the Ministry of Education of Hunan University。
文摘We report an unprecedented C-H bond functionalization of cyclopropenes enabled by dinuclear gold catalysis.Highly selective C-H allylation,alkynylation and halogenation of cyclopropenes with organic halides have been realized.The reaction does not require strong external oxidants and affords access to functionalized cyclopropenes in moderate to good yields.The reductive elimination process to controllably construct C-C or C-X bonds can be tuned by using different dinuclear gold catalysts.
基金the financial support from the National Natural Science Foundation of China(grant nos.22001117,21971108,21971111,and 21732003)the Natural Science Foundation of Jiangsu Province(grant no.BK20190006)+1 种基金Fundamental Research Funds for the Central Universities(0205/14380252),“Innovation&Entrepreneurship Talents Plan”of Jiangsu ProvinceFoundation of Advanced Catalytic Engineering Research Center of the Ministry of Education of Hunan University.
文摘Ketones serve as one of the most critical building blocks in organic synthesis,involving numerous functional group transformations.Herein,we rep ort an unprecedented photoredox-nickel metallap hotoredox-catalyzed decarboxylative acylation of common aliphatic acids with readily available aromatic and aliphatic thioesters.A wide range of structurally diverse asymmetrical aryl alkyl and dialkyl ketones have been constructed in yields of up to 98% with this strategy.The protocol has excellent reaction selectivity and functional group compatibility,representing a significant step forward in ketone synthesis.The one-pot decarboxylative acylation at the gram scale from two different carboxylic acids and the late-stage application for the synthesis of complex ketones shows its synthetic robustness.Both mechanistic experiments and density functional theory(DFT)calculations suggest that the decarboxylative acylation reaction operates via an underdeveloped Ni(Ⅰ)-Ni(Ⅱ)-Ni(Ⅰ)-Ni(Ⅲ)-Ni(Ⅰ)catalytic cycle.
基金the support by the National Natural Science Foundation of China (No. 11672016)
文摘As a key component of electro-optical systems, a Two-axis Scan mirror AssemblY(TSAY) is usually used for Line-of-Sight(LOS) precision pointing, tracking, scanning, and stabilizing. Therefore, it is necessary for a TSAY to have a large angular range, high dynamic characteristics, and small mirror surface distortion. Furthermore, vibration from carriers of electro-optical systems, such as spacecraft and airplanes, is inevitable, so it is critical to guarantee the control accuracy of a TSAY under vibration. In this paper, a TSAY prototype is designed and developed. To increase the control bandwidth, structural topology optimization is applied to the TSAY’s elliptical mirror to reduce the moment of inertia, meanwhile keeping surface flatness. A flexible hinge is adopted to achieve a large angular range. To suppress the angular perturbation caused by the base linear vibration, an adaptive feedforward loop with base-integrated Micro-Electro-Mechanical System(MEMS) accelerators is constructed to enhance the TSAY’s feedback loop. Simulation and experimental results show that the TSAY prototype’s two-axis mechanical angular ranges are more than ±3.2°, the mirror surface flatness Root Mean Square(RMS) value is better than 0.04 k, and the closed-loop bandwidth is beyond 330 Hz. These are suitable for most applications. Besides, the angular perturbation caused by the base vibration can be suppressed more than 37.7% with the addition of the adaptive feedforward loop.
