Pulsed excitation of cold atmospheric plasmas is commonly believed to offer valuable benefits compared to the mainstream sinusoidal excitation. However, direct comparison of pulsed and sinusoidal atmospheric plasmas remains few, if any, thus casting an uncertainty of whether pulsed excitation facilitates any significant advantage. In this letter, we report a comparison study of pulsed and sinusoidal cold atmospheric plasma jets through electrical characterization, gas temperature measurement, and optical detection of reactive plasma species. An example of pulsed excitation is shown to reduce the electrical energy consumption by a factor of 12 for producing the same amount of oxygen atoms.

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Product quality problem is a critical issue for multistage manufacturing processes, especially in continuous production lines whereby quality characteristics are measured at the end of the line. Therefore, it is important to reduce process variation by identifying its sources and eliminating its causes. In this regard, a novel approach, to identify the source of variation in multistage manufacturing processes through integration of the Fisher's linear discriminant analysis and the stream of variation methodology, is proposed. Linear discriminant analysis separates the variation of the quality characteristics through the manufacturing process stages while the stream of variation methodology is used for variation propagation modeling in multistage manufacturing processes. Finally, the future deviation is assigned into the analysis in order to identify the source of variation. With an illustrative case study, it is concluded that the proposed approach improves fault diagnosis of continuous production lines in multistage manufacturing processes.

This paper presents a methodology for diagnostics of fixture failures in multistage manufacturing processes (MMP). The diagnostic methodology is based on the state-space model of the MMP process, which includes part fixturing layout geometry and sensor location. The state space model of the MMP characterizes the propagation of fixture fault variation along the production stream, and is used to generate a set of predetermined fault variation patterns. Fixture faults are then isolated by using mapping procedure that combines the Principal Component Analysis (PCA) with pattern recognition approach. The fault diagnosability conditions for three levels: (a) within single station, (b) between stations, and (c) for the overall process, are developed. The presented analysis integrates the state space model of the process and matrix perturbation theory to estimate the upper bound for isolationability of fault pattern vectors caused by correlated and uncorrelated noises. A case study illustrates the proposed method. �DOI: 10.1115/1.1445155

Conventional radio-frequency (rf) nonthermal atmospheric plasmas are generated in a millimeter gap. In this Letter, we present a self-consistent numerical study of rf atmospheric microplasmas in a submillimeter gap comparable to their sheath thickness. It is shown that the narrow electrode gap deforms the discharge structure, ultimately removing the bulk-plasma region and disabling electron trapping. Significantly, these properties permit rf atmospheric microplasmas to operate at very high current densities thus simultaneously achieving higher stability and greater chemical reactivity.

An experimental observation of fast-moving plasma bullets produced in an atmospheric dielectric-barrier discharge jet is reported in this paper. Nanosecond imaging suggests that the atmospheric discharge jet consists of a plasma bullet train traveling at a hypersonic speed from 7.0km∕sto43.1km∕s. Yet on a millisecond scale, the bullet train appears as a plasma jet of several centimeters long. The plasma bullets are produced through several possible mechanisms, the most likely of which is related to the ionization wave. Time and space resolved optical emission spectroscopy show that reactive plasma species can be delivered to different spatial sites with varying quantities.

Citation: DENG X.T., SHI, J.J. and KONG, M.G., 2007. Protein destruction by a helium atmospheric pressure glow discharge: capability and mechanisms.Journal of Applied Physics, 101 (7), article 074701, pp.1-9.Additional Information:• Biological sterilization represents one of the most exciting applications of atmospheric pressure glow discharges ͑APGD͒. Despite the fact that surgical instruments are contaminated by both microorganisms and proteinaceous matters, sterilization effects of APGD have so far been studied almost exclusively for microbial inactivation. This work presents the results of a detailed investigation of the capability of a helium-oxygen APGD to inactivate proteins deposited on stainless-steel surfaces. Using a laser-induced fluorescence technique for surface protein measurement, a maximum protein reduction of 4.5 logs is achieved by varying the amount of the oxygen admixture into the background helium gas. This corresponds to a minimum surface protein of 0.36 femtomole/ mm 2 . It is found that plasma reduction of surface-borne protein is through protein destruction and degradation, and that its typically biphasic reduction kinetics is influenced largely by the thickness profile of the surface protein. Also presented is a complementary study of possible APGD protein inactivation mechanisms. By interplaying the protein inactivation kinetics with optical emission spectroscopy, it is shown that the main protein-destructing agents are excited atomic oxygen ͑via the 777 and 844 nm emission channels͒ and excited nitride oxide ͑via the 226, 236, and 246 nm emission channels͒. It is also demonstrated that the most effective protein reduction is achieved possibly through a synergistic effect between atomic oxygen and nitride oxide. This study is a useful step toward a full confirmation of the efficacy of APGD as a sterilization technology for surgical instruments contaminated by prion proteins.

Aims:  To determine the effects of surface cell concentration and phase of growth on the inactivation of Escherichia coli cells using an atmospheric nonthermal plasma. Methods and Results:  Cells of E. coli K12 were deposited onto the surface of membrane filters and exposed to the plume from a cold atmospheric gas plasma. Scanning electron microscopy revealed severe loss in structural integrity of plasma‐treated cells, and optical emission spectra indicated that inactivation was brought about by reactive plasma species. The survival of E. coli cells was found to depend on the cell surface density: as the surface density increased from 107 to 1011 CFU cm−2, the rate constant in the Baranyi inactivation model decreased from 19·59 to 1·03 min−1. Cells harvested from mid‐exponential, late exponential and stationary phases of growth displayed differences in their resistances to the effects of the plasma however, exponential phase cells were not more susceptible than those from the stationary phase. Conclusions:  High surface concentrations of cells affects the penetration of plasma species and treatment effectiveness. The physiological state of cells, as determined by phase of growth, affects their resistance to plasma inactivation. Significance and Impact of the Study:  In designing inactivation treatments, surface concentration and cell physiology need to be taken into account.