Kinetic effects of nanosecond discharge on ignition delay time

The effects of nanosecond discharge on ignition characteristics of a stoichiometric methane–air mixture without inert diluent gas were studied by numerical simulation at 0.1 MPa and an initial temperature of 1300 K. A modified non-equilibrium plasma kinetic model was developed to simulate the temporal evolution of particles produced during nanosecond discharge and its afterglow. As important roles in ignition, path fluxes of O and H radicals were analyzed in detail. Different strength of E/N and different discharge duration were applied to the discharge process in this study. And the results presented that a deposited energy of 1–30 m J·cm^(-3) could dramatically reduce the ignition delay time. Furthermore, temperature and radicals analysis was conducted to investigate the effect of non-equilibrium plasma on production of intermediate radicals. Finally, sensitivity analysis was employed to have further understanding on ignition chemistries of the mixture under nanosecond discharge.

Experimental Study on Triggering Characteristics of a Surface Flashover Triggered Vacuum Switch

Triggering characteristics of triggered vacuum switch （TVS）, including the discharge delay time, delay jitter, range of operational voltage and peak of pulsed current, are investigated. Both structure and experimental circuit of TVS are presented. The results indicate that TVS, as a surface flashover triggering device with high dielectric permittivity material, is with excellent triggering characteristics. When the hold-off voltage reaches 120 kV, the minimum operational voltage is 1.3 kV, and the minimum discharge delay time and jitter are 100 ns and ±10 ns, respectively. The peak current is up to 240 kA when the operational voltage reaches 100 kV. TVS can well satisfy the main demands of high voltage and current applications, and can also be used under a multi-crowbar circuit.

Experimental Research of ZnO Surface Flashover Trigger Device of Pseudo-Spark Switch

Pseudo-spark switch（PSS） is one of the most widely used discharge switches for pulse power technology.It has many special characteristics such as reliability in a wide voltage range,small delay time,as well as small delay jitter.In this paper,the measuring method for the initial plasma of ZnO surface flashover triggering device of PSS is studied and the results of the measurement show that the electron emission charge is mainly influenced by trigger voltage,gas pressure and DC bias voltage.When the bias voltage increases from 2 kV to 6 kV with the gap distancc fixed at 3 mm,the electron emission charge changes from 2 μC to about 6μC.When the gap distance changes from 3 mm to 5 mm with the bias voltage fixed at 2 kV,the electron emission charge increases from 1.5 μC to 2.5μC.When the gap distance is 4 mm,the hold-off voltage of PSS is 45 kV at gas pressure of 2 Pa,the minimum operating voltage is less than 1 kV.So,the operating scope is from 2.22%to 99%of its self-breakdown voltage.The discharging delay time decreases from 450 ns to 150 ns when the trigger pulse voltage is 1 kV and the discharging voltage is changed from 1 kV to 12 kV.When the trigger pulse voltage is 6 kV,the discharging delay time is less than 100 ns and changes from 100 ns to 50 ns,and the delay jitters are less than30 ns.

A Retrospective Study of the Epidemiologic and Clinical Characteristics of COVID-19 Among Hospitalized Patients in Quanzhou,China

Coronavirus disease 2019(COVID-19)has spread throughout China.However,information about COVID-19 in cities and regions outside Wuhan is limited and the indicators that predict the length of hospital stay for patients with COVID-19 are unclear.Therefore,we collected clinical data from 47 patients with COVID-19 in Quanzhou City.The median age was 38 years[interquartile range(IQR):31–50 years],and 24(51%)were male.There were 8 mild,36 moderate,and 3 severe/critical cases.The median interval from exposure to disease onset was 13 days(IQR:8–18 days).The incidence of severe/critical cases was 33%(3/10)in patients with hypertension.Common symptoms included fever(83%),cough(77%),fatigue(40%),a sore,dry throat(28%),and diarrhea(21%).One patient(2%)developed respiratory distress syndrome on day 13 of inpatient treatment.Six patients had leukopenia,17 had elevated C-reactive protein(CRP),and 8 had lymphocytopenia and elevated lactate dehydrogenase(LDH).The median length of hospitalization was 22 days(IQR:16-30 days).Dynamic monitoring of LDH,CRP,and neutrophil-lymphocyte ratio predicted whether length of hospitalization would exceed 21 days.Most patients presented with mild and moderate disease.Patients with hypertension were more likely to become severe or critical.Dynamic monitoring of LDH,CRP,and neutrophil-lymphocyte ratio levels can help predict delayed discharge from the hospital.