Develop Guidelines for Pavement Preservation Treatments and for Building a Pavement Preservation Program Platform for Alaska

INE/AUTC 12.0

1D Fluid model of RF-Excited Cold Atmospheric Plasmas in Helium with Air Gas Impurities

Cold atmospheric plasmas (CAPs) in helium with air gas impurities (HeþAir for abbreviation) compromise the discharge stability of helium and the chemical reactivity of air, having great prospects for various applications such as plasma biomedicine. However, different kinds of reactive species are produced in HeþAir CAPs but only a few of them could be measured, and the plasma chemistry is so complex that the reported simulation models are simplified to a large extent, such as neglecting the space variation of CAPs by using a 0D model. As a result, much remains unknown for HeþAir CAPs, which hinders the development of their applications. For that reason, a 1D fluid model of HeþAir CAPs is developed in this paper, incorporating 48 chemical species and 118 volume reactions, which are extracted from a complex chemistry set by a reported 0D model, and then the density distribution of reactive species, the power dissipation pathways, and the chemistry pathways among the reactive species are obtained as a function of air concentration from 500 to 10 000 ppm. It is found that O and NO are the dominant reactive oxygen species (ROS) and reactive nitrogen species (RNS), respectively. Taking the ROS as a whole, it is mainly produced by the electron impact dissociation and excitation of O2; taking the RNS as a whole, it is mainly produced by the oxidation of atomic nitrogen [N and N(2D)], and NO is the precursor for all the other RNS

Temporal Modulation of Plasma Species in Atmospheric Dielectric Barrier Discharges

The atmospheric pressure dielectric barrier discharge in helium is a pulsed discharge in nature and the moment of maximum species densities is almost consistent with peak discharge current density. In this paper, a one-dimensional fluid model is used to investigate the temporal structure of plasma species in an atmospheric He-N2 dielectric barrier discharge (DBD). It is demonstrated that there exist microsecond delays of the moments of the maximum electron and ion densities from the peak of discharge current density. These time delays are caused by a competition between the electron impact and Penning ionizations, modulated by the N2 level in the plasma-forming gas. Besides, significant electron wall losses lead to the DBD being more positively charged and, with a distinct temporal separation in the peak electron and cation densities, the plasma is characterized with repetitive bursts of net positive charges. The temporal details of ionic and reactive plasma species may provide a new idea for some biological processes

Quantifying the Concentration and Penetration Depth of Long-Lived RONS in Plasma Activated Water by UV Absorption Spectroscopy

Reactive oxygen and reactive nitrogen species (RONS) are believed to play a key role in biomedical applications, which means that RONS must reach the target tissue to produce a therapeutic effect. Existing methods (electron spin spectrometry and microplate reading) to determine the RONS concentration are not suitable for experimental real-time measurements because they require adding an indicating reagent to the plasma-treated medium, which may alter the chemical composition of the medium. In this paper, we propose a method to measure the long-lived RONS concentration in plasma-activated water (PAW) by using UV absorption spectroscopy. Based on an analysis and fit of the absorption spectra of standard solutions (H2O2, NaNO2, and NaNO3), we propose a detailed fitting procedure that allows us to calculate the concentrations of simplex H2O2, NO2−, and NO3−. The results show that the pH and the cross reactivity between RONS in PAW correlate strongly with the absorption spectra. To confirm the accuracy of the calculations, we also use a microplate reader and add chemical reagents to measure the concentrations of H2O2, NO2−, and NO3−. The results show that the concentrations calculated by the proposed fitting method are relatively accurate and that the error range is acceptable. Additionally, the time-dependent diffusion of RONS in PAW is measured and analyzed at different depths in the PAW. This fitting approach constitutes a nonintrusive approach to measure RONS at different depths in PAW

Investigation on the RONS and Bactericidal Effects Induced by He + O2 Cold Plasma Jets: In Open Air and in an Airtight Chamber

He + O2 plasma jets in open air and in an airtight chamber are comparatively studied, with respect to their production of gaseous/aqueous reactive species and their antibacterial effects. Under the same discharge power, the plasma jet in open air has higher densities of gaseous reactive species and a higher concentration of aqueous H2O2 but lower concentrations of aqueous OH and O2-. In addition, the increase in the O2 ratio in He in both plasma jets causes a linear decrease in the population of gaseous reactive species, except for O(3p5P) when a small amount of O2 is added to the working gas. The concentrations of aqueous reactive species for OH and H2O2 also drop monotonically with the increase in additive O2, while the aqueous O2- first increases and then decreases. Moreover, it is interesting that the bactericidal inactivation in the airtight chamber condition is much greater than that in the open air condition regardless of the presence or absence of additive O2 in the He plasma jet. The concentration trends of O2- for both the plasma jets are similar to their antibacterial effects, and little antibacterial effect is achieved when a scavenger of O2- is used, indicating that O2- should be a main antibacterial agent. Moreover, it should not be O2- alone to achieve the antibacterial effect, and some reactive nitrogen species such as ONOO- and O2NOO- might also play an important role

Interfacial Current Distribution Between Helium Plasma Jet and Water Solution

The plasma-liquid interaction holds great importance for a number of emerging applications such as plasma biomedicine, yet a main fundamental question remains about the nature of the physiochemical processes occurring at the plasma-liquid interface. In this paper, the interfacial current distribution between helium plasma jet and water solution was measured for the first time by means of the splitting electrode method, which was borrowed from the field of arc plasma. For a plasma plume in continuous mode, it was found that the mean absolute current distribution at the plasma-liquid interface typically had an annular shape. This shape could be affected by regulating the air doping from the surrounding atmosphere, the gas flow rate, the applied voltage and the conductivity of the water solution. However, only the air doping fraction and the water conductivity could fundamentally change the interfacial current distribution from the annular shape to the central maximum shape. It was deduced that a certain amount of ambient air doping (mainly N2 and O2) and a low conductivity (typically \u3c 300 μS/cm) of the treated water were essential for the formation of the annular current distribution at the plasma-liquid interface

The Mechanism of Plasma Plume Termination for Pulse Excited Plasmas in a Quartz Tube

Although the formation and propagation of plasma plume for atmospheric pressure plasmas have been intensively studied, how does the plasma plume terminate is still little known. In this letter, helium plasma plumes are generated in a long quartz tube by pulsed voltages and a constant gas flow. The voltages have a variable pulse width (PW) from 0.5 μs to 200 μs. It is found that the plasma plume terminates right after the falling edge of each voltage pulse when PW \u3c 20 μs, whereas it terminates before the falling edge. When PW is larger than 30 μs, the duration of plasma plume starts to decrease, and the termination is found to occur at the current zero moment of the discharge current through the high-voltage electrode, which is much different from that through the ground electrode. This indicates that part of the discharge current is shunted by the plasma plume to its downstream gas region. An equivalent circuit model is developed, from which the surface charge deposited on the quartz tube is found crucial for accelerating the termination of a plasma plume when PW \u3e 30 μs

Comparison Between the Water Activation Effects by Pulsed and Sinusoidal Helium Plasma Jets

Comparisons between pulsed and sinusoidal plasma jets have been extensively reported for the discharge characteristics and gaseous reactive species, but rarely for the aqueous reactive species in water solutions treated by the two types of plasma jets. This motivates us to compare the concentrations of aqueous reactive species induced by a pulsed and a sinusoidal plasma jet, since it is widely reported that these aqueous reactive species play a crucial role in various plasma biomedical applications. Experimental results show that the aqueous H2O2, OH/O2−, and O2−/ONOO− induced by the pulsed plasma jet have higher concentrations, and the proportional difference increases with the discharge power. However, the emission intensities of OH(A) and O(3p5P) are higher for the sinusoidal plasma jet, which may be attributed to its higher gas temperature since more water vapor could participate in the plasma. In addition, the efficiency of bacterial inactivation induced by the pulsed plasma jet is higher than that for the sinusoidal plasma jet, in accordance with the concentration relation of aqueous reactive species for the two types of plasma jets. Published by AIP Publishing

Production and Correlation of Reactive Oxygen and Nitrogen Species in Gas- and Liquid-Phase Generated by Helium Plasma Jets Under Different Pulse Widths

In this paper, we present the effects of the pulse width (PW) on the plasma jet\u27s discharge characteristics, particularly focusing on the production and correlation of the reactive oxygen and nitrogen species (RONS) in gas- and liquid-phase. It is found that the length of plasma jet plume first increases before the PW of 10 μs, then gradually decreases and finally almost remains unchanged beyond 150 μs. The plasma bullet disappears after the falling edge of the voltage pulse at low PW, while it terminates far ahead of the falling edge of voltage pulse at high PW. This is mainly attributed to accumulation of space charges that lead to weakening of the reduced electric field with an increase of PW from low to high. More important, it is found that the excited reactive species, the positive and negative ions from plasma jet, and the concentrations of NO2– and NO3– in deionized water exposed to plasma jet so display the first increasing and then decreasing change trend with increase of PW, while the concentration of H2O2 in water almost displays the linearly increasing trend. This mainly results from the formation of the H3O+ and HO2–, as well as their ion water clusters that can produce more OH radicals to be converted into H2O2, while the NO2– and NO3– in gas phase can transport into water and exist most stably in water. The water cluster formation at gas-liquid interface is an important key process that can affect the chemical nature and dose of aqueous RONS in water; this is beneficial for understanding how the RONS are formed in liquid-phase. Published by AIP Publishing

Alkaline Plasma-Activated Water (PAW) as an Innovative Therapeutic Avenue for Cancer Treatment

Plasma-activated water (PAW) is considered to be an effective anticancer agent due to the diverse aqueous reactive oxygen and nitrogen species (RONS: ROS and RNS), but the drawback of low dose and short duration of RONS in acidified PAW limits their clinical application. Herein, this Letter presents an innovative therapeutic avenue for cancer treatment with highly-effective alkaline PAW prepared by air surface plasma. This anticancer alkaline formulation is comprised of a rich mixture of highly chemical RONS and exhibited a prolonged half-life compared to acidified PAW. The H2O2, NO2-, and ONOO-/O2- concentrations in the alkaline PAW can reach up to 18-, 16-, and 14-fold higher than that in acidic PAW, and the half-life of these species was extended over 8-, 10-, and 26-fold, respectively. The synergistic potent redox action between these RONS with alkaline pH was shown to be more potent than acidic PAW for cancer cell inhibition in vitro. Furthermore, the alkaline PAW injection treatment also significantly inhibited tumor growth in tumor-bearing mice. The possible reasons are that the alkaline PAW would disturb the acid extracellular milieu leading to the inhibition of tumor growth and progression; moreover, the efficient and durable RONS with alkaline pH could induce significant cell apoptosis by altering cell biomolecules and participating apoptosis-related signaling pathways. These findings offer promising applications for developing a strategy with real potential for tumor treatment in clinical applications