We use microscopic Monte Carlo simulation techniques to investigate the impact of H_(2)diffusion energy on the recombination efficiency of H_(2)on interstellar dust grain surfaces under diffuse and translucent cloud c...We use microscopic Monte Carlo simulation techniques to investigate the impact of H_(2)diffusion energy on the recombination efficiency of H_(2)on interstellar dust grain surfaces under diffuse and translucent cloud conditions.We constructed five models representing different possible conditions encountered by adsorbed H and H_(2)on interstellar dust grains.We implemented adsorption sites with multiple binding energies for surface species;the Encounter-Desorption mechanism was also included.The study focused on silicate surfaces in diffuse clouds and water ice surfaces in translucent clouds.The results show that the recombination efficiency of H_(2)on dust surfaces decreases as H_(2)diffusion energy increases.An interesting finding of this work is that considering different binding sites for H and H_(2)gives rise to multiple steady phases,during which the recombination efficiency remains constant with a change in H_(2)diffusion energy.展开更多
There have been several studies on sulfur depletion in dense cores like TMC-1(Taurus Molecular Cloud 1),employing updated reaction networks for sulfur species to explain the missing sulfur in the gas within dense clou...There have been several studies on sulfur depletion in dense cores like TMC-1(Taurus Molecular Cloud 1),employing updated reaction networks for sulfur species to explain the missing sulfur in the gas within dense clouds.Most of these studies used a C/O ratio of 0.7 or lower.We present NSRT(NanShan 26m Radio Telescope)observations of TMC-1 alongside results from time-dependent chemical simulations using an updated chemical network.Our findings highlight the impact of the C/O ratio on the gas-phase evolution of C2S and C3S.The simulation results show that the C/O ratio is an important parameter,playing a fundamental role in determining the gas-phase abundances of sulfur species in dense cores.展开更多
Beam lifetime is dominated by Touschek scattering at the Shanghai Synchrotron Radiation Facility(SSRF).Touschek loss rate is affected by probability for scattering beyond the RF acceptance and the volume charge densit...Beam lifetime is dominated by Touschek scattering at the Shanghai Synchrotron Radiation Facility(SSRF).Touschek loss rate is affected by probability for scattering beyond the RF acceptance and the volume charge density of the bench.In the phaseⅡupgrade of the SSRF,a third harmonic superconducting cavity will be used to enhance the Touschek lifetime by lengthening the bunches.The Touschek lifetime improvement factor is affected by the voltage of a harmonic cavity.To stabilize the cavity voltage,a tuning control system was designed to control it.The design of the tuning control system was based on the SSRF third-generation low-level RF control system.Some hardware and specialized algorithms were redesigned to fit the harmonic cavity control.The design of the tuning control system is complete,and the control system has been tested.The test result shows that the fluctuation of amplitude is<±0.34%within 1.5 h,which satisfies the stability requirement.展开更多
The Shanghai High Repetition Rate XFEL and Extreme Light Facility(SHINE)project will use 6001.3 GHz fundamental power couplers,which are modified based on TTF-Ⅲ power couplers,for continuous-wave operation with input...The Shanghai High Repetition Rate XFEL and Extreme Light Facility(SHINE)project will use 6001.3 GHz fundamental power couplers,which are modified based on TTF-Ⅲ power couplers,for continuous-wave operation with input power up to approximately 7 kW.The first batch of 20 sets of 1.3 GHz coupler prototypes was fabricated from three domestic manufacturers for the SHINE project.To better characterize the radio frequency conditioning phenomena for validating the performance of power couplers,a room temperature test stand was designed,constructed,and commissioned for the SHINE 1.3 GHz power couplers.In addition,a horizontal test cryostat was built to test the 1.3 GHz superconducting cavities,fundamental power couplers,tuners,and other components as a set.The results of these tests indicate that the 1.3 GHz couplers are capable of handling up to 14 kW continuous waves.Herein,the main aspects of the radio frequency design and construction of the test stand,along with the test results of the high-power conditioning of the 1.3 GHz couplers,are described.展开更多
A digital transfer function measurement system has been embedded in the low-level radio frequency (LLRF) system of the storage ring of the Shanghai Synchrotron Radiation Facility. The measurement results indicate that...A digital transfer function measurement system has been embedded in the low-level radio frequency (LLRF) system of the storage ring of the Shanghai Synchrotron Radiation Facility. The measurement results indicate that the decreased control accuracy at high current is primarily owing to ripples from the high-voltage power supply, the transient beam loading effect, and the digital aliasing effect. The current LLRF algorithm is not able to suppress these disturbances.展开更多
The kinetic Monte Carlo simulation is a rigorous numerical approach to study the chemistry on dust grains in cold dense interstellar clouds. By tracking every single reaction in chemical networks step by step, this ap...The kinetic Monte Carlo simulation is a rigorous numerical approach to study the chemistry on dust grains in cold dense interstellar clouds. By tracking every single reaction in chemical networks step by step, this approach produces more precise results than other approaches but takes too much computing time. Here we present a method of a new data structure, which is applicable to any physical conditions and chemical networks, to save computing time for the Monte Carlo algorithm. Using the improved structure,the calculating time is reduced by 80 percent compared with the linear structure when applied to the osu-2008 chemical network at 10K. We investigate the effect of the encounter desorption in cold cores using the kinetic Monte Carlo model with an accelerating data structure. We found that the encounter desorption remarkably decreases the abundance of grain-surface H2 but slightly influences the abundances of other species on the grain.展开更多
Astrochemistry has made great progress in recent years.Especially the grain surface chemistry played important roles in the explanation of the formation of the interstellar molecules.In this review,we will discuss the...Astrochemistry has made great progress in recent years.Especially the grain surface chemistry played important roles in the explanation of the formation of the interstellar molecules.In this review,we will discuss the progress,including the di erent numerical methods to simulate the ice mantles in the astrochemical models.We will also introduce the laboratory astrochemical experimental results,and their contributions to the grain surface chemistry in the review.展开更多
At low temperatures(10 K),hydrogen atoms can diffuse quickly on grain ice mantles and frequently encounter hydrogen molecules,which cover a notable fraction of grain surface.The desorption energy of H atoms on H2 subs...At low temperatures(10 K),hydrogen atoms can diffuse quickly on grain ice mantles and frequently encounter hydrogen molecules,which cover a notable fraction of grain surface.The desorption energy of H atoms on H2 substrates is much less than that on water ice.The H atom encounter desorption mechanism is adopted to study the enhanced desorption of H atoms on H_(2 )substrates.Using a small reaction network,we show that the steady-state surface H abundances predicted by the rate equation model that includes H atom encounter desorption agree reasonably well with the results from the more rigorous microscopic Monte Carlo method.For a full gas-grain model,H atom encounter desorption can reduce surface H abundances.Therefore,if a model adopts the encounter desorption of H atoms,it becomes more difficult for hydrogenation products such as methanol to form,but it is easier for C,O and N atoms to bond with each other on grain surfaces.展开更多
High-density housing can be interpreted as collections of individual units, which inevitably results in the dilemma between the global standardization designed by architects and local customization implemented by user...High-density housing can be interpreted as collections of individual units, which inevitably results in the dilemma between the global standardization designed by architects and local customization implemented by users. However, it is impossible to reflect the users＇ various needs in the conceptual design stage for high-density housing because of the economic, industrial and time constrains. In response to this challenge, this research paper outlines a different high-density housing design approach that can adopt users＇ individual customization in the conceptual design stage during the housing design practice. Hence, the design process would be an open-ended evolutionary and transparent process rather than deterministic executions as we have now in most high-density cities, such as Hong Kong. In order to overcome the deficiency in addressing future uncertainties of different users and address the issues of one-off developments without iterating users＇ feedback in the housing practice, this essay proposes IOSDA （integrated open source design for architecture） for the design practice of high-density housing, through collective data and parametric connectivity between users and architects. IOSDA reflects a different design attitude towards the future, i.e., to shift from architects＇ heroic prediction of the future to collective engagement of the present with more robust capacities for new possibilities.展开更多
基金supported by the National Natural Science Foundation of China(No.12173023)the Xinjiang Tianchi Talent Program(2024)。
文摘We use microscopic Monte Carlo simulation techniques to investigate the impact of H_(2)diffusion energy on the recombination efficiency of H_(2)on interstellar dust grain surfaces under diffuse and translucent cloud conditions.We constructed five models representing different possible conditions encountered by adsorbed H and H_(2)on interstellar dust grains.We implemented adsorption sites with multiple binding energies for surface species;the Encounter-Desorption mechanism was also included.The study focused on silicate surfaces in diffuse clouds and water ice surfaces in translucent clouds.The results show that the recombination efficiency of H_(2)on dust surfaces decreases as H_(2)diffusion energy increases.An interesting finding of this work is that considering different binding sites for H and H_(2)gives rise to multiple steady phases,during which the recombination efficiency remains constant with a change in H_(2)diffusion energy.
基金supported by the Natural Science Foundation of Xinjiang Uygur Autonomous Region (Grant No. 2022D01B221)he Xinjiang Tianchi Talent Program (2023)+4 种基金the NSRT operators for their assistance during the observationspartly supported by the OperationMaintenance and Upgrading Fund for Astronomical Telescopes and Facility Instrumentsbudgeted from the Ministry of Finance of China and administrated by the Chinese Academy of Sciencesthe Urumqi Nanshan Astronomy and Deep Space Exploration Observation and Research Station of Xinjiang (Grant No. XJYWZ2303)
文摘There have been several studies on sulfur depletion in dense cores like TMC-1(Taurus Molecular Cloud 1),employing updated reaction networks for sulfur species to explain the missing sulfur in the gas within dense clouds.Most of these studies used a C/O ratio of 0.7 or lower.We present NSRT(NanShan 26m Radio Telescope)observations of TMC-1 alongside results from time-dependent chemical simulations using an updated chemical network.Our findings highlight the impact of the C/O ratio on the gas-phase evolution of C2S and C3S.The simulation results show that the C/O ratio is an important parameter,playing a fundamental role in determining the gas-phase abundances of sulfur species in dense cores.
文摘Beam lifetime is dominated by Touschek scattering at the Shanghai Synchrotron Radiation Facility(SSRF).Touschek loss rate is affected by probability for scattering beyond the RF acceptance and the volume charge density of the bench.In the phaseⅡupgrade of the SSRF,a third harmonic superconducting cavity will be used to enhance the Touschek lifetime by lengthening the bunches.The Touschek lifetime improvement factor is affected by the voltage of a harmonic cavity.To stabilize the cavity voltage,a tuning control system was designed to control it.The design of the tuning control system was based on the SSRF third-generation low-level RF control system.Some hardware and specialized algorithms were redesigned to fit the harmonic cavity control.The design of the tuning control system is complete,and the control system has been tested.The test result shows that the fluctuation of amplitude is<±0.34%within 1.5 h,which satisfies the stability requirement.
基金supported by Shanghai Municipal Science and Technology Major Project(No.2017SHZDZX02)。
文摘The Shanghai High Repetition Rate XFEL and Extreme Light Facility(SHINE)project will use 6001.3 GHz fundamental power couplers,which are modified based on TTF-Ⅲ power couplers,for continuous-wave operation with input power up to approximately 7 kW.The first batch of 20 sets of 1.3 GHz coupler prototypes was fabricated from three domestic manufacturers for the SHINE project.To better characterize the radio frequency conditioning phenomena for validating the performance of power couplers,a room temperature test stand was designed,constructed,and commissioned for the SHINE 1.3 GHz power couplers.In addition,a horizontal test cryostat was built to test the 1.3 GHz superconducting cavities,fundamental power couplers,tuners,and other components as a set.The results of these tests indicate that the 1.3 GHz couplers are capable of handling up to 14 kW continuous waves.Herein,the main aspects of the radio frequency design and construction of the test stand,along with the test results of the high-power conditioning of the 1.3 GHz couplers,are described.
文摘A digital transfer function measurement system has been embedded in the low-level radio frequency (LLRF) system of the storage ring of the Shanghai Synchrotron Radiation Facility. The measurement results indicate that the decreased control accuracy at high current is primarily owing to ripples from the high-voltage power supply, the transient beam loading effect, and the digital aliasing effect. The current LLRF algorithm is not able to suppress these disturbances.
基金supported by the CAS “Light of West China Program” (2017-QNXZ-B)Youth Innovation Promotion Association CAS+3 种基金the Heaven Lake Hundred-Talent Program of Xinjiang Uygur Autonomous Region of Chinathe National Natural Science Foundation of China (Nos. 11673054 11873082, U1531125, 11803080, 11503075, 11543002, 11673054 and 11703075)the National Key Basic Research Program of China (973 Program 2015CB857100)the National Key Basic Research and Development Program (2018YFA0404704)
文摘The kinetic Monte Carlo simulation is a rigorous numerical approach to study the chemistry on dust grains in cold dense interstellar clouds. By tracking every single reaction in chemical networks step by step, this approach produces more precise results than other approaches but takes too much computing time. Here we present a method of a new data structure, which is applicable to any physical conditions and chemical networks, to save computing time for the Monte Carlo algorithm. Using the improved structure,the calculating time is reduced by 80 percent compared with the linear structure when applied to the osu-2008 chemical network at 10K. We investigate the effect of the encounter desorption in cold cores using the kinetic Monte Carlo model with an accelerating data structure. We found that the encounter desorption remarkably decreases the abundance of grain-surface H2 but slightly influences the abundances of other species on the grain.
基金the National Natural Science Foundation of China(No.11673054)Xinjiang Tianchi Bairen Project.
文摘Astrochemistry has made great progress in recent years.Especially the grain surface chemistry played important roles in the explanation of the formation of the interstellar molecules.In this review,we will discuss the progress,including the di erent numerical methods to simulate the ice mantles in the astrochemical models.We will also introduce the laboratory astrochemical experimental results,and their contributions to the grain surface chemistry in the review.
基金funded by the National Natural Science Foundation of China(Grant Nos.11673054,11973075 and 11973099)。
文摘At low temperatures(10 K),hydrogen atoms can diffuse quickly on grain ice mantles and frequently encounter hydrogen molecules,which cover a notable fraction of grain surface.The desorption energy of H atoms on H2 substrates is much less than that on water ice.The H atom encounter desorption mechanism is adopted to study the enhanced desorption of H atoms on H_(2 )substrates.Using a small reaction network,we show that the steady-state surface H abundances predicted by the rate equation model that includes H atom encounter desorption agree reasonably well with the results from the more rigorous microscopic Monte Carlo method.For a full gas-grain model,H atom encounter desorption can reduce surface H abundances.Therefore,if a model adopts the encounter desorption of H atoms,it becomes more difficult for hydrogenation products such as methanol to form,but it is easier for C,O and N atoms to bond with each other on grain surfaces.
文摘High-density housing can be interpreted as collections of individual units, which inevitably results in the dilemma between the global standardization designed by architects and local customization implemented by users. However, it is impossible to reflect the users＇ various needs in the conceptual design stage for high-density housing because of the economic, industrial and time constrains. In response to this challenge, this research paper outlines a different high-density housing design approach that can adopt users＇ individual customization in the conceptual design stage during the housing design practice. Hence, the design process would be an open-ended evolutionary and transparent process rather than deterministic executions as we have now in most high-density cities, such as Hong Kong. In order to overcome the deficiency in addressing future uncertainties of different users and address the issues of one-off developments without iterating users＇ feedback in the housing practice, this essay proposes IOSDA （integrated open source design for architecture） for the design practice of high-density housing, through collective data and parametric connectivity between users and architects. IOSDA reflects a different design attitude towards the future, i.e., to shift from architects＇ heroic prediction of the future to collective engagement of the present with more robust capacities for new possibilities.
