Junna Li

Xi'an Jiaotong University

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Aici Qiu

Xi'an Jiaotong University

Fan Guo

Northwest Institute of Nuclear Technology

Weiqing Chen

King Fahd University of Petroleum and Minerals

Wei Jia

Northwest Institute of Nuclear Technology

Junping Tang

Dalian University

Daohong Zhang

South Central University for Nationalities

Linshen Xie

Northwest Institute of Nuclear Technology

Aiqing Zhang

Second Affiliated Hospital of Nanjing Medical University

Haiyang Wang

University of Electronic Science and Technology of China

Yongliang Wang

Xi'an Jiaotong University

Cooperative Institutions

Xi'an Jiaotong University

Northwest Institute of Nuclear Technology

Chinese Academy of Sciences

Shaanxi Normal University

Jilin University

Huazhong University of Science and Technology

University of Chinese Academy of Sciences

State Key Laboratory of Electrical Insulation and Power Equipment

Shanghai Jiao Tong University

First Hospital of Jilin University

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Compact pulse generator with sub-nanosecond rise time based on inductance of order of several nH

Review of Scientific Instruments (2022)

Junna Li Yongliang Wang Shi He Xuliang Chen Aici Qiu

Pulse generators with a sub-nanosecond rise time are typically used to calibrate measurement probes in electromagnetic pulses. However, the technological dilemma between high voltage and low inductance has not been adequately addressed in this context. In this paper, the authors investigate the effects of the circuit and structural parameters on the generator. To reduce the rise time of the output voltage of the generator to a few hundred picoseconds, the inductance of its structure and the spark gap needs to be strictly controlled. We use SF6 at 1 MPa as an insulating gas for the spark gap to reduce the inductance of the capacitor and the switch to the order of several nH. The results of theoretical calculations and simulations were used to design and test two generators that used a coaxial ceramic capacitor and three plate ceramic capacitors, respectively. The experimental results showed that a double-exponential pulse voltage with a sub-nanosecond rise time could be obtained in a 50 Ω transmission line in both generators. The generator with the coaxial ceramic capacitor had better characteristics than the one that used three plate ceramic capacitors with a rise time of 630-860 ps when the peak output voltage was in the range of 5-30 kV.

Rise time

Spark gap

Marx Generator

Nanosecond

Ceramic capacitor

Coaxial

10.1063/5.0101573

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Citations (1)

The leakage field characteristics of a large hybrid electromagnetic pulse simulator

Review of Scientific Instruments (2024)

Q. Huang Junna Li Fangzheng Wu Shiji Li Yuhan Gong

The leakage field of a hybrid electromagnetic pulse simulator with horizontal polarization is simulated and experimentally investigated based on the finite integration technique in this paper. The field distribution characteristics and far-field radiation pattern of the simulator are given. The attenuation characteristics of the electric field at specific directions in the z = 2 m plane are also predicted by numerical data fitting. Finally, according to the ICNIRP guidelines, the safe distances that satisfy the occupational and public exposure limits are obtained, and the safety regions lower than the reference levels are given. Results show that the electric field in the α = 0° direction is mainly contributed by the main polarization component (Ey), while the total electric field in the α = 90° direction also requires consideration of the vertical component (Ez). The dominant radiation direction in the z = 2 m plane lies between α = 0° and 30°, which poses the highest demand for the safe distance around the simulator. In addition, impedance mismatch and ground reflection are the main factors affecting the waveforms of the radiated electric field.

Electromagnetic pulse

Leakage (economics)

10.1063/5.0211559

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A dual-waveband dynamic IR scene projector based on DMD

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2016)

Yu Hu Yawei Zheng Jiaobo Gao Kefeng Sun Junna Li

Infrared scene simulation system can simulate multifold objects and backgrounds to perform dynamic test and evaluate EO detecting system in the hardware in-the-loop test. The basic structure of a dual-waveband dynamic IR scene projector was introduced in the paper. The system's core device is an IR Digital Micro-mirror Device (DMD) and the radiant source is a mini-type high temperature IR plane black-body. An IR collimation optical system which transmission range includes 3~5μm and 8~12μm is designed as the projection optical system. Scene simulation software was developed with Visual C++ and Vega soft tools and a software flow chart was presented. The parameters and testing results of the system were given, and this system was applied with satisfying performance in an IR imaging simulation testing.

Digital Light Processing

10.1117/12.2246636

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DC電スイッチにおける混合ガス破壊特性【JST・京大機械翻訳】

Qiangjiguang yu Lizishu (2016)

He Shi Junna Li Guo Fan Weiqing Chen Aici Qiu

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The effects of pulse voltage rise time on the nanosecond pulsed breakdown of nitrogen spark switch at atmospheric pressure with 3D PIC-MCC model

Physics of Plasmas (2023)

Yongliang Wang Junna Li Ming Jiang Qisheng Li Chunan Li

In this paper, the effects of pulse voltage rise time on the nanosecond pulsed breakdown of the nitrogen spark switch at atmospheric pressure are analyzed. Based on the assumption of initial electrons generation due to the field emission, the simulations are performed using a three-dimensional particle-in-cell, Monte Carlo-collision model for the pulse voltage with a rise time of 40, 60, and 100 ns, respectively. The breakdown experiments of the nitrogen spark switch are carried out for three different rise times. The results obtained are as follows. First, the nanosecond pulsed breakdown of the switch includes the formation and fast propagation of the streamer, which depend on the multiplication of the electron avalanche, and the intense ionization due to photoelectrons and energetic electrons, respectively. Second, with the rise time of pulse voltage increasing, the generation of runaway electrons becomes more difficult and the streamer branches, which are mainly caused by photoionization and captured energetic electrons, become more obvious. Finally, the breakdown time delay of the switch becomes shorter and the breakdown voltage becomes higher at the same pressure for the decreasing rise time of pulse voltage, which is consistent with the measurement results.

Nanosecond

Rise time

Photoelectric effect

Spark gap

Streamer discharge

10.1063/5.0138011

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Citations (4)

Project of Upgrading Beijiang River(From Wushi Reach to Sanshui River Mouth) to Grade III Navigation Channel

Pearl River (2010)

Junna Li

The three outstanding problems in the Beijiang River 1 000 t navigation channel regulation project,namely improving the shoals around the reservoir area,construction of secondary ship lock and the inadequate navigation clearance dimension were analyzed.The engineering countermeasures were figured out to solve these problems,providing the projects of this kind with the positive reference.

Lock (firearm)

Shoal

River mouth

Source

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Self-Assembly of Amido-Ended Hyperbranched Polyester Films with a Highly Ordered Dendritic Structure

ACS Applied Materials & Interfaces (2014)

Daohong Zhang Zhicai Xu Junna Li Sufang Chen Juan Cheng

Self-assemblies fabricated from dendrimers and amphiphilic polymers have demonstrated remarkable performances and a wide range of applications. Direct self-assembly of hyperbranched polymers into highly ordered macrostructures with heat-resistance remains a big challenge due to the weak amphiphilicity of the polymers. Here, we report the self-assembly of amphiphilic amido-ended hyperbranched polyester (HTDA-2) into millimeter-size dendritic films using combined hydrogen bond interaction and solvent induction. The self-assembly process and mechanism have been studied. Hydrogen bond interaction between amido-ended groups assists the aggregation of inner and outer chains of the HTDA-2, resulting in phase separation and micelle formation. Some micelles attach to and grow on the glass substrate like seedlings. Other micelles move to the seedlings and connect with their branches via solvent induction and hydrogen bond interaction, leading to the fabrication of highly ordered crystalline dendritic films that show high heat-resistance. HTDA-2 can further self-assemble into sheet crystals on the dendritic films.

10.1021/am504705c

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Citations (12)

Lower PTEN may be associated with CD8+ T cell exhaustion in diffuse large B-cell lymphoma

Human Immunology (2023)

Shutao Zheng Jiajia Ma Junna Li Xuelian Pang Mingfu Ma

TIGIT

10.1016/j.humimm.2023.07.007

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Design of dual-channel infrared collimating projection optic system

Journal of Applied Optics (2019)

Zheng Yawei Junna Li Gao Zedong Jianjun Li Jiaobo Gao

Collimated light

10.5768/jao201940.0101010

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Design of Compact Field Distortion Gas Spark Gap Switch with Low Inductance

Gaoya dianqi (2008)

Junna Li

Gas spark switch is a key component of the pulsed power technology.A compact field distortion gas spark gap with low inductance is deigned and tested.Through optimization of the structure,the axial dimension of the switch is shortened and thus the low inductance can be obtained.The experimental results indicate that in dry air conditions,when switching coefficient is 70%,the breakdown delay is 90 ns and the utter is about 10 ns.

Spark gap

SPARK (programming language)

Distortion (music)

Pulsed Power

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