Non-oxidative conversion of methane to olefins,aromatics and hydrogen(MTOAH) has been reported recently over metal single sites such as iron and platinum.The reaction was proposed to involve catalytic activation of me...Non-oxidative conversion of methane to olefins,aromatics and hydrogen(MTOAH) has been reported recently over metal single sites such as iron and platinum.The reaction was proposed to involve catalytic activation of methane followed by gas phase C-C coupling of methyl radicals.This study using H atom Rydberg Tagging time-of-flight technique provides direct experimental evidence for the formation of hydrogen radicals during MTOAH reaction over a catalytic quartz wall reactor containing embedded iron species(denoted as Fe-reactor).Fe-reactor gives 7.3% methane conversion at 1273 K with 41.2% selectivity toward C2(ethane,ethylene and acetylene) and 31.8% toward BTX(benzene,toluene and xylene),respectively.The enhancing effects of hydrogen radicals on overall MTOAH performance are validated by cofeeding hydrogen donor benzene,which provides an additional route of methane activation apart from catalytic activation.展开更多
We propose optical experiments to study the depth of field for a thermal light lensless ghost imaging system. It is proved that the diaphragm is an important factor to influence the depth of field, and the ghost image...We propose optical experiments to study the depth of field for a thermal light lensless ghost imaging system. It is proved that the diaphragm is an important factor to influence the depth of field, and the ghost images of two detected objects with longitudinal distance less than the depth of field can be achieved simultaneously. The longitudinal coherence scale of the thermal light lensless ghost imaging determines the depth of field. Theoretical analysis can well explain the experimental results.展开更多
With the development of technology in aerospace,medical devices and other fields,high-performance difficult-tomachine materials have been widely used in these fields due to their good comprehensive mechanical properti...With the development of technology in aerospace,medical devices and other fields,high-performance difficult-tomachine materials have been widely used in these fields due to their good comprehensive mechanical properties.However,when using traditional machining methods,it is difficult to ensure the machining accuracy and surface quality,and at the same time,there are problems such as serious tool wear and low machining efficiency.Laserassisted machining(LAM)technology is an advanced manufacturing process that softens the material in the machining area through the preheating effect of the laser,thus reducing the surface hardness of the material and improving the machinability of the material,which has the advantages of high efficiency and economy in machining difficult-tomachine materials.This paper introduces the common methods of establishing thermal models and simulation modeling of removal behavior in the LAM material removal process,summarizes the research progress on the removal behavior of LAM processing of various difficult-to-machine materials,and analyzes the shortcomings and challenges of the current research.Finally,the key issues of LAM material removal mechanism are proposed,and the development direction of LAM material removal technology is envisioned in order to provide a reference for the research and development in this field.展开更多
Light(sub-GeV)dark matter has gained increasing interest in terms of direct detection.Accelerated dark matter is a promising candidate that can generate detectable nuclear recoil energy within the sub-GeV range.Becaus...Light(sub-GeV)dark matter has gained increasing interest in terms of direct detection.Accelerated dark matter is a promising candidate that can generate detectable nuclear recoil energy within the sub-GeV range.Because of the large kinetic energy,its interactions with the nucleus are predominantly governed by inelastic scattering,including quasi-elastic and deep inelastic scattering.In this work,we calculated the inelastic effects in dark matter-Earth scattering mediated by a vector particle.Our analysis revealed that the impact of inelastic scattering relies on the mediator mass and the kinetic energy spectrum of dark matter.The results exhibited considerable disparity:the upper bounds of the exclusion limit for the spin-independent cross-section between accelerated dark matter and nuclei via a heavy mediator differ by several tens of times when inelastic scattering is considered.展开更多
基金supported by the Chinese Academy of Sciences (XDB10020202)the National Natural Science Foundation of China (Grant Nos. 21621063, 21425312, 21761132035)the National Key R&D Program of China (2017YFA0403402)。
文摘Non-oxidative conversion of methane to olefins,aromatics and hydrogen(MTOAH) has been reported recently over metal single sites such as iron and platinum.The reaction was proposed to involve catalytic activation of methane followed by gas phase C-C coupling of methyl radicals.This study using H atom Rydberg Tagging time-of-flight technique provides direct experimental evidence for the formation of hydrogen radicals during MTOAH reaction over a catalytic quartz wall reactor containing embedded iron species(denoted as Fe-reactor).Fe-reactor gives 7.3% methane conversion at 1273 K with 41.2% selectivity toward C2(ethane,ethylene and acetylene) and 31.8% toward BTX(benzene,toluene and xylene),respectively.The enhancing effects of hydrogen radicals on overall MTOAH performance are validated by cofeeding hydrogen donor benzene,which provides an additional route of methane activation apart from catalytic activation.
基金Supported by the Beijing Natural Science Foundation under Grant No 4133086the Fundamental Research Funds for th Central Universities under Grant No 2-9-2014-022
文摘We propose optical experiments to study the depth of field for a thermal light lensless ghost imaging system. It is proved that the diaphragm is an important factor to influence the depth of field, and the ghost images of two detected objects with longitudinal distance less than the depth of field can be achieved simultaneously. The longitudinal coherence scale of the thermal light lensless ghost imaging determines the depth of field. Theoretical analysis can well explain the experimental results.
基金supported by the National Natural Science Foundation of China(No.52175377)the Natural Science Foundation of Chongqing(No.CSTB2022NSCO-LZX0080)+2 种基金the Innovation Group Science Fund of Chongqing Natural Science Foundation(No.stc2019jcyj-cxttX0003)the Basic Research Funds for Central Universities(No.2023CDJXY-026 and No.2023CDJXY-021)Funded by Open Fund of State Key Laboratory of Mechanical Transmission,China(SKLMT-MSKFKT-202215).
文摘With the development of technology in aerospace,medical devices and other fields,high-performance difficult-tomachine materials have been widely used in these fields due to their good comprehensive mechanical properties.However,when using traditional machining methods,it is difficult to ensure the machining accuracy and surface quality,and at the same time,there are problems such as serious tool wear and low machining efficiency.Laserassisted machining(LAM)technology is an advanced manufacturing process that softens the material in the machining area through the preheating effect of the laser,thus reducing the surface hardness of the material and improving the machinability of the material,which has the advantages of high efficiency and economy in machining difficult-tomachine materials.This paper introduces the common methods of establishing thermal models and simulation modeling of removal behavior in the LAM material removal process,summarizes the research progress on the removal behavior of LAM processing of various difficult-to-machine materials,and analyzes the shortcomings and challenges of the current research.Finally,the key issues of LAM material removal mechanism are proposed,and the development direction of LAM material removal technology is envisioned in order to provide a reference for the research and development in this field.
基金supported by the National Natural Science Foundation of China(Grant Nos.12275134,12275232,and 12335005)。
文摘Light(sub-GeV)dark matter has gained increasing interest in terms of direct detection.Accelerated dark matter is a promising candidate that can generate detectable nuclear recoil energy within the sub-GeV range.Because of the large kinetic energy,its interactions with the nucleus are predominantly governed by inelastic scattering,including quasi-elastic and deep inelastic scattering.In this work,we calculated the inelastic effects in dark matter-Earth scattering mediated by a vector particle.Our analysis revealed that the impact of inelastic scattering relies on the mediator mass and the kinetic energy spectrum of dark matter.The results exhibited considerable disparity:the upper bounds of the exclusion limit for the spin-independent cross-section between accelerated dark matter and nuclei via a heavy mediator differ by several tens of times when inelastic scattering is considered.
