An impact point prediction(IPP) guidance based on supervised learning is proposed to address the problem of precise guidance for the ballistic missile in high maneuver penetration condition.An accurate ballistic traje...An impact point prediction(IPP) guidance based on supervised learning is proposed to address the problem of precise guidance for the ballistic missile in high maneuver penetration condition.An accurate ballistic trajectory model is applied to generate training samples,and ablation experiments are conducted to determine the mapping relationship between the flight state and the impact point.At the same time,the impact point coordinates are decoupled to improve the prediction accuracy,and the sigmoid activation function is improved to ameliorate the prediction efficiency.Therefore,an IPP neural network model,which solves the contradiction between the accuracy and the speed of the IPP,is established.In view of the performance deviation of the divert control system,the mapping relationship between the guidance parameters and the impact deviation is analysed based on the variational principle.In addition,a fast iterative model of guidance parameters is designed for reference to the Newton iteration method,which solves the nonlinear strong coupling problem of the guidance parameter solution.Monte Carlo simulation results show that the prediction accuracy of the impact point is high,with a 3 σ prediction error of 4.5 m,and the guidance method is robust,with a 3 σ error of 7.5 m.On the STM32F407 singlechip microcomputer,a single IPP takes about 2.374 ms,and a single guidance solution takes about9.936 ms,which has a good real-time performance and a certain engineering application value.展开更多
The Accelerator Driven Sub-critical(ADS)system is a strategic plan to solve the nuclear waste problem for nuclear power plants in China.High-energy particle accelerators and colliders contain long strings of supercond...The Accelerator Driven Sub-critical(ADS)system is a strategic plan to solve the nuclear waste problem for nuclear power plants in China.High-energy particle accelerators and colliders contain long strings of superconducting devices,superconducting radio frequency cavities,and magnets,which may require cooling by 2 K superfluid helium(HeliumⅡ).2 K superfluid helium cryogenic system has become a research hot spot in the field of superconducting accelerators.In this study,the ADS Injector-I 2 K cryogenic system is examined in detail.The cryogenic system scheme design,key equipment,and technology design,such as the 2 K Joule–Thomson(J–T)heat exchanger and cryomodules CM1+CM2 design,are examined,in addition to the commissioning and operation of the cryogenic system.The ADS Injector-I 2 K cryogenic system is the first 100 W superfluid helium system designed and built independently in China.The ADS proton beam reached 10 Me V at 10 m A in July 2016 and 10 Me V at 2 m A in continuous mode in January 2017 and has been operated reliably for over 15,000 h,proving that the design of ADS Injector-I 2 K cryogenic system,the key equipment,and technology research are reasonable,reliable,and meet the requirements.The research into key technologies provides valuable engineering experience that can be helpful for future projects such as CI-ADS(China Initiative Accelerator-Driven System),SHINE(Shanghai High Repetition Rate XFEL and Extreme Light Facility),PAPS(Platform of Advanced Photon Source Technology),and CEPC(Circular Electron-Positron Collider),thereby developing national expertise in the field of superfluid helium cryogenic systems.展开更多
BACKGROUND Biliary adenofibroma(BF)is a rare benign epithelial tumor with the possibility of malignant transformation.Its main pathological feature is a well-defined cystic or honeycomb mass.BF has no specific clinica...BACKGROUND Biliary adenofibroma(BF)is a rare benign epithelial tumor with the possibility of malignant transformation.Its main pathological feature is a well-defined cystic or honeycomb mass.BF has no specific clinical manifestations or laboratory and imaging findings;thus,it is easily misdiagnosed before surgery.This report describes a case in which biliary cystadenoma was misdiagnosed preoperatively and BF was diagnosed postoperatively.The imaging features,particularly the magnetic resonance imaging(MRI)features,were analyzed and summarized.CASE SUMMARY A 68-year-old Chinese man was admitted to our hospital with a 2-mo history of abdominal discomfort.Following admission to our hospital,laboratory examinations showed normal tumor marker concentrations and liver function.Hepatocellular carcinoma was considered after contrast-enhanced ultrasound examination.MRI suggested the possibility of cystadenoma of the bile duct.However,postoperative pathological examination confirmed the diagnosis of BF.No local recurrence was found 1 mo after surgery.CONCLUSION Our objective is to highlight the imaging diagnostic value of BF,especially on an MRI enhanced scan with gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid.展开更多
One of the most important devices for the High Energy Photon Source Test Facility project,the 2.6 T 32-pole 3W1 superconducting wiggler,was designed by the Institute of High Energy Physics(IHEP);its magnetic gap is 68...One of the most important devices for the High Energy Photon Source Test Facility project,the 2.6 T 32-pole 3W1 superconducting wiggler,was designed by the Institute of High Energy Physics(IHEP);its magnetic gap is 68 mm,and its storage energy is 286 kJ.It will be installed at the storage ring of the Beijing Electron Positron Collider Upgrade Project at the IHEP to replace the old permanent wiggler.The primary purpose of the cryostat is to create a safe and reliable system and realize long-term operation with zero liquid helium consumption.To maintain liquid helium temperature,four identical two-stage cryocoolers are placed symmetrically at the wiggler ends.The cryostat has only one 60 K thermal shield,which is used to reduce the heat load to the liquid helium vessel.The cryostat has several novel features,including a suspension system with little heat leakage that is self-centered during cooling of the cryostat,a special copper liner and high-efficiency condensers,three pairs of binary current leads,and three-level safety design.The cryogenic system has been cooled three times,and the residual cooling capacity is approximately 0.41 W at 4.2 K without current.展开更多
Impact statement Habitat loss has been a primary threat to biodiversity.However,species do not function in isolation but often associate with each other and form complex networks.Thus,revealing how the network complex...Impact statement Habitat loss has been a primary threat to biodiversity.However,species do not function in isolation but often associate with each other and form complex networks.Thus,revealing how the network complexity and stability scale with habitat area will give us more insights into the effects of habitat loss on ecosystems.In this study,we explored the relationships between the island area and the network complexity and stability of soil microbes.We found that the complexity and stability of soil microbial co‐occurrence networks scale positively with island area,indicating that habitat loss will potentially simplify and destabilize soil microbial networks.展开更多
A framework was proposed to identify a comprehensive set of aerodynamic admittance functions for bridge decks. The contributions of the cross-spectra between longitudinal and vertical wind velocity components and betw...A framework was proposed to identify a comprehensive set of aerodynamic admittance functions for bridge decks. The contributions of the cross-spectra between longitudinal and vertical wind velocity components and between turbulence components and gust-induced forces were embedded in the identification procedure. To facilitate application of the identified functions in engineering practice, the concept of an equivalent aerodynamic admittance function was introduced and numerically validated. The equivalent aerodynamic admittance functions of a set of streamlined and bluff cross sections were identified experimentally in a wind tunnel. Buffeting analysis of a bridge deck was carried out and the response predicted using the identified aerodynamic admittance functions compared well with the measured response. In addition, a sensitivity analysis was performed to delineate the influence of aerodynamic and structural parameters on the buffeting response, thereby demonstrating the significance of the proposed identification framework.展开更多
We propose and discuss terahertz(THz) electro-optic modulator induced by periodically patterned graphene microcavity. Due to the joint effect of graphene plasmon resonances and Fabry-Perot(F-P) oscillations, plasmon-i...We propose and discuss terahertz(THz) electro-optic modulator induced by periodically patterned graphene microcavity. Due to the joint effect of graphene plasmon resonances and Fabry-Perot(F-P) oscillations, plasmon-induced transparency(PIT) effect is achieved and the operation frequency can be dynamically tuned by graphene Fermi energies and structural parameters. The results reveal that modulation depth(MD) larger than 80% is obtained across a wide frequency range from 4.2 THz to 9.4 THz, and the largest MD and Q factor reaches 95% and 15.8, respectively. In addition, operation frequency range and MD can also be tuned by optimizing the structure parameters. This investigation promises the development of high-performance widely tunable THz modulator in chip integrated photonic circuits.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.62103432)supported by Young Talent fund of University Association for Science and Technology in Shaanxi, China(Grant No.20210108)。
文摘An impact point prediction(IPP) guidance based on supervised learning is proposed to address the problem of precise guidance for the ballistic missile in high maneuver penetration condition.An accurate ballistic trajectory model is applied to generate training samples,and ablation experiments are conducted to determine the mapping relationship between the flight state and the impact point.At the same time,the impact point coordinates are decoupled to improve the prediction accuracy,and the sigmoid activation function is improved to ameliorate the prediction efficiency.Therefore,an IPP neural network model,which solves the contradiction between the accuracy and the speed of the IPP,is established.In view of the performance deviation of the divert control system,the mapping relationship between the guidance parameters and the impact deviation is analysed based on the variational principle.In addition,a fast iterative model of guidance parameters is designed for reference to the Newton iteration method,which solves the nonlinear strong coupling problem of the guidance parameter solution.Monte Carlo simulation results show that the prediction accuracy of the impact point is high,with a 3 σ prediction error of 4.5 m,and the guidance method is robust,with a 3 σ error of 7.5 m.On the STM32F407 singlechip microcomputer,a single IPP takes about 2.374 ms,and a single guidance solution takes about9.936 ms,which has a good real-time performance and a certain engineering application value.
文摘The Accelerator Driven Sub-critical(ADS)system is a strategic plan to solve the nuclear waste problem for nuclear power plants in China.High-energy particle accelerators and colliders contain long strings of superconducting devices,superconducting radio frequency cavities,and magnets,which may require cooling by 2 K superfluid helium(HeliumⅡ).2 K superfluid helium cryogenic system has become a research hot spot in the field of superconducting accelerators.In this study,the ADS Injector-I 2 K cryogenic system is examined in detail.The cryogenic system scheme design,key equipment,and technology design,such as the 2 K Joule–Thomson(J–T)heat exchanger and cryomodules CM1+CM2 design,are examined,in addition to the commissioning and operation of the cryogenic system.The ADS Injector-I 2 K cryogenic system is the first 100 W superfluid helium system designed and built independently in China.The ADS proton beam reached 10 Me V at 10 m A in July 2016 and 10 Me V at 2 m A in continuous mode in January 2017 and has been operated reliably for over 15,000 h,proving that the design of ADS Injector-I 2 K cryogenic system,the key equipment,and technology research are reasonable,reliable,and meet the requirements.The research into key technologies provides valuable engineering experience that can be helpful for future projects such as CI-ADS(China Initiative Accelerator-Driven System),SHINE(Shanghai High Repetition Rate XFEL and Extreme Light Facility),PAPS(Platform of Advanced Photon Source Technology),and CEPC(Circular Electron-Positron Collider),thereby developing national expertise in the field of superfluid helium cryogenic systems.
文摘BACKGROUND Biliary adenofibroma(BF)is a rare benign epithelial tumor with the possibility of malignant transformation.Its main pathological feature is a well-defined cystic or honeycomb mass.BF has no specific clinical manifestations or laboratory and imaging findings;thus,it is easily misdiagnosed before surgery.This report describes a case in which biliary cystadenoma was misdiagnosed preoperatively and BF was diagnosed postoperatively.The imaging features,particularly the magnetic resonance imaging(MRI)features,were analyzed and summarized.CASE SUMMARY A 68-year-old Chinese man was admitted to our hospital with a 2-mo history of abdominal discomfort.Following admission to our hospital,laboratory examinations showed normal tumor marker concentrations and liver function.Hepatocellular carcinoma was considered after contrast-enhanced ultrasound examination.MRI suggested the possibility of cystadenoma of the bile duct.However,postoperative pathological examination confirmed the diagnosis of BF.No local recurrence was found 1 mo after surgery.CONCLUSION Our objective is to highlight the imaging diagnostic value of BF,especially on an MRI enhanced scan with gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid.
基金supported by the High Energy Photon Source Test Facility(HEPS-TF)project。
文摘One of the most important devices for the High Energy Photon Source Test Facility project,the 2.6 T 32-pole 3W1 superconducting wiggler,was designed by the Institute of High Energy Physics(IHEP);its magnetic gap is 68 mm,and its storage energy is 286 kJ.It will be installed at the storage ring of the Beijing Electron Positron Collider Upgrade Project at the IHEP to replace the old permanent wiggler.The primary purpose of the cryostat is to create a safe and reliable system and realize long-term operation with zero liquid helium consumption.To maintain liquid helium temperature,four identical two-stage cryocoolers are placed symmetrically at the wiggler ends.The cryostat has only one 60 K thermal shield,which is used to reduce the heat load to the liquid helium vessel.The cryostat has several novel features,including a suspension system with little heat leakage that is self-centered during cooling of the cryostat,a special copper liner and high-efficiency condensers,three pairs of binary current leads,and three-level safety design.The cryogenic system has been cooled three times,and the residual cooling capacity is approximately 0.41 W at 4.2 K without current.
基金This research was supported by the National Natural Science Foundation of China(31971553,32222051,and 31361123001)the National Science Foundation of the United States of America(DEB-1342754 and DEB-1856318)+1 种基金the Shanghai Rising-Star ProgramP.W.was supported by the research fund of the post-doctor who came to Shenzhen(szbo202306).
文摘Impact statement Habitat loss has been a primary threat to biodiversity.However,species do not function in isolation but often associate with each other and form complex networks.Thus,revealing how the network complexity and stability scale with habitat area will give us more insights into the effects of habitat loss on ecosystems.In this study,we explored the relationships between the island area and the network complexity and stability of soil microbes.We found that the complexity and stability of soil microbial co‐occurrence networks scale positively with island area,indicating that habitat loss will potentially simplify and destabilize soil microbial networks.
基金the National Natural Science Foundation of China(NSFC31971553,32222051and32061143014)the Shanghai Rising-Star Program(20QA1402900)the Fundamental Research Funds for the Central Universities and the Open Fund for Key Lab.of Land Degradation and Ecological Restoration in northwestern China of Ningxia University(LDER2023Z01).
基金supported by the National Natural Science Foundation of China(No.51778495)the National Key Research and Development Program of China(No.2017YFB1201204)。
文摘A framework was proposed to identify a comprehensive set of aerodynamic admittance functions for bridge decks. The contributions of the cross-spectra between longitudinal and vertical wind velocity components and between turbulence components and gust-induced forces were embedded in the identification procedure. To facilitate application of the identified functions in engineering practice, the concept of an equivalent aerodynamic admittance function was introduced and numerically validated. The equivalent aerodynamic admittance functions of a set of streamlined and bluff cross sections were identified experimentally in a wind tunnel. Buffeting analysis of a bridge deck was carried out and the response predicted using the identified aerodynamic admittance functions compared well with the measured response. In addition, a sensitivity analysis was performed to delineate the influence of aerodynamic and structural parameters on the buffeting response, thereby demonstrating the significance of the proposed identification framework.
基金Supported by Scientific Research Plan Projects of Shaanxi Education Department(203011730)
文摘We propose and discuss terahertz(THz) electro-optic modulator induced by periodically patterned graphene microcavity. Due to the joint effect of graphene plasmon resonances and Fabry-Perot(F-P) oscillations, plasmon-induced transparency(PIT) effect is achieved and the operation frequency can be dynamically tuned by graphene Fermi energies and structural parameters. The results reveal that modulation depth(MD) larger than 80% is obtained across a wide frequency range from 4.2 THz to 9.4 THz, and the largest MD and Q factor reaches 95% and 15.8, respectively. In addition, operation frequency range and MD can also be tuned by optimizing the structure parameters. This investigation promises the development of high-performance widely tunable THz modulator in chip integrated photonic circuits.
