Junxiang Liu

Inactivation of a 25.5 µm Enterococcus faecalis biofilm by a room-temperature, battery-operated, handheld air plasma jet

Effective biofilm inactivation using a handheld, mobile plasma jet powered by a 12 V dc battery and operated in open air without any external gas supply is reported. This cold, room-temperature plasma is produced in self-repetitive nanosecond discharges with current pulses of ~100 ns duration, current peak amplitude of ~6 mA and repetition rate of ~20 kHz. It is shown that the reactive plasma species penetrate to the bottom layer of a 25.5 µm-thick Enterococcus faecalis biofilm and produce a strong bactericidal effect. This is the thickest reported biofilm inactivated using room-temperature air plasmas.

Multiple plasma bullet behavior of an atmospheric-pressure plasma plume driven by a pulsed dc voltage

The dynamics of an atmospheric-pressure plasma plume generated in a controlled gas environment are studied. It is found that, at a particular pulse width, two or three plasma bullets are generated in each voltage pulse for both positive and negative voltage pulses. The velocities of the multiple bullets are more than four and less than fourteen times those in the case of a single bullet, for positive and negative voltage pulses, respectively. A detailed analysis shows that the charges carried by the bullets probably play an important role in the propagation of plasma bullets and in the formation of multiple bullets. It is found that the electrode polarity also plays an important role in the generation and propagation of multiple plasma bullets.

Grain boundaries and low-field transport properties in colossal magnetoresistance materials

The grain-boundary structure and the temperature dependence of resistivity were investigated for (1-x)LCMO + xYSZ, where LCMO and YSZ represent La2/3Ca1/3MnO3 and yttria-stabilized zirconia, respectively. It is shown that the YSZ doped samples for x 2%. The metal-insulator transition temperature (Tp) decreases for x 2% as x is increased. LFMR increases with x for x 2%. The experimental observations are discussed on the basis of scanning electron microscopy (SEM) analysis, which reveals YSZ appearing at the grain boundaries of LCMO for x 2%.

A battery-operated atmospheric-pressure plasma wand for biomedical applications

Summary form only given. A handheld, battery-operated atmospheric-pressure plasma rod (named plasma wand, Fig. 1) which does not rely on external power source (e.g., wall power or power generator) and gas supply is reported1. The plasma wand can be used for killing bacteria, fungi, or viruses that are hidden in narrow channels such as nasal cavity and ear canal, which are difficult to access using most of currently available devices. Besides, the electrical characterization, plasma wand temperature, emission spectra of the plasma, ozone and OH radical concentration generated by the device, are investigated by different diagnostic methods. The temperature on the plasma wand stays at about 38°C after operating for about 5 minute and the outside electrode is grounded. So there is no feeling of hot or electrical shock at all when we hold the plasma wand. From the Lissajous-figure of the discharge, the power consumption is estimated to be about 12 W. The ozone concentration reaches 120 ppm at 1 mm away from the device and the OH concentration reaches 3.5×1014 cm-3 in the plasma. The preliminary bacteria inactivation experiment results show that all bacteria samples on the microfiltration membrane are killed by this device within 30 s.

An investigation on two-phase mixture discharges: the effects of macroparticle sizes

A two-phase mixture (TPM) is a mixture of gas and macroparticles of high concentration, and there has been significant interest in many technical applications and natural phenomena concerning two-phase mixture discharges (TPMDs), but until now there has been no widely accepted analysis for the propagation of discharges in TPMs. In this paper, 21 kinds of different dielectric materials are used to investigate the effects on TPMD. The diameters of macroparticles in 21 kinds of TPMs are measured by microscope, laser particle size analyzer, etc, and the volume fractions are measured by a video camera and particle image velocimetry system. Based on a direct comparison of the breakdown voltages and the percentages of the discharge path in TPMs with those in air, this work reveals that whether TPMs promote the discharge development or not depends mainly on the macroparticle sizes. These macroparticles in TPMs distort the electric field, interact with ions, electrons or photons, and produce corresponding enhancements or decreases in ionization and excitation as the streamer front encounters them, but the details of alterations on the discharge development are highly correlated with the macroparticle sizes.

Initiation and Propagation of Discharge in Liquid Droplets: Effect of Droplet Sizes

Three kinds of water mist with different droplet sizes are applied to understand the effect of droplet sizes on the initiation and propagation of discharges in a nonuniform field at atmospheric pressure. Based on the measurement of droplet sizes in three mists and the volume fraction of water droplets, effect of droplet sizes is demonstrated by directly comparing the percentages of the discharge path in mist at the different positions with those in air. It can be concluded that the mist with smaller μm-droplets has the negative impact on the initiation and propagation of discharges; the mist with larger μm-droplets has the inhibited effect on the starting and growth of positive discharge but has the contrary effects on negative discharge.

The Research on Pulsed Arc Electrohydraulic Discharge With Discharge Electrode and Its Application to Removal of Bacteria

With the rapid expansion of urbanization, the technology of wastewater treatment has an increasingly crucial role in the field of environmental protection science and technology. The technology of pulsed arc electrohydraulic discharge (PAED) has been studied in depth by virtue of its signally treatment effect, low power consumption, and so on. The experiments were carried out with the wastewater from cyclic activated sludge system tank. The 10-L PAED reactor with eccentric electrodes is designed as industrialization mode. The PAED power supply is 3 kJ/pulse and the discharge rate is 2 Hz. The experiments on different distances, radii, and types of water gap electrodes were carried out. Three different electrode materials (titanium, tungsten, and titanium alloy) were used in the PAED system in the experiments. The results show that the sterilization effect on Escherichia coli is the highest when the material of the water gap electrodes is tungsten and the cumulative input electrical power is 1000 Wh/m3. Fundamental discharge characteristics linked with disinfection performance will be discussed in detail in this paper.

Effect of A-site deficiency on electrical transport properties of YSZ doped manganites

Abstract The electrical transport properties of the composite samples: A-site stoichiometry (1−x)La2/3Ca1/3MnO3+xYSZ and A-site deficiency (1−x)(La2/3Ca1/3)0.95MnO3+xYSZ with different YSZ percentage x were investigated, respectively. The similar metal–insulator transition at different temperature TP was observed in the two types of composite samples: With increasing of the YSZ percentage, the zero-field resistivity of the composite samples increases and TP shifts to the low temperature for the range of x 2%. For the same YSZ percentage x, TP of (1−x)La2/3Ca1/3MnO3+xYSZ is lower than that of (1−x)(La2/3Ca1/3)0.95MnO3+xYSZ. The different effects between the two type composites were also observed in the nonlinear current–voltage (I–V) behaviors. The results suggest that A-site deficiency and YSZ dopant can be used to adjust purposely the metal–insulator transition temperature and resistivity of composites.

Measurement of reactive species density in the battery-operated, handheld room temperature atmospheric plasma jet for biomedical applications

Room temperature atmospheric pressure plasma jets (RTAPP-Js) have widespread biomedical and health care applications in pathogen inactivation, wound healing, blood coagulation, and interventional oncology, to mention just a few. The overwhelming majority of the existing RTAPP-Js rely on external power (e.g., generators or wall power) and gas feed (e.g., He or Ar gas) supply. This limits their utility in mobile handheld devices for point-of-care applications, e.g., in natural disaster rescue and military combat operations, treatments in remote locations, etc. Moreover, treatment efficacy of such devices should be comparable or superior to current equipment. Recently, Pei et al. have developed a handheld RTAPP-Js (named “Plasma Flashlight”) powered by a 12 V DC battery1. The plasma source does not rely on any external power or feedstock gas supplies. In this report, we quantitative measured the O3 density of the Plasma Flashlight by absorption spectroscopy which was performed with a standard mercury lamp. Atom O and OH radicals that play a crucial role in the inactivation process were measured using the laser-induced fluorescence (LIF) technology. The distribution of Atom O and OH radicals in the plasma plum was also studied.

An economical fabrication technique for SIMOX using plasma immersion ion implantation

Buried oxide layers in Si were fabricated using non-mass analyzed plasma immersion ion implantation (PIII). The implantation was carried out by applying a large negative bias to a Si wafer immersed in an oxygen plasma and a dose of 3/spl times/10/sup 17/ cm/sup -2/ of oxygen was implanted in about three minutes. Cross section transmission electron microscopy (XTEM) and Rutherford backscattering spectrometry (RES) were used to characterize the wafers. Our results indicate that a continuous buried oxide layer with a single crystal silicon overlayer was synthesized.