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End date: 2021 × Start date: 2021 × DDC: 530 × Type: Text × WGL Institute: INP ×

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Now showing 1 - 10 of 25
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    Microwave plasma discharges for biomass pretreatment: Degradation of a sodium carboxymethyl cellulose model
    (New York, NY : American Inst. of Physics, 2020) Honnorat, B.; Brüser, V.; Kolb, J.F.
    Biogas production is an important component of an environmentally benign renewable energy strategy. However, the cost-effectiveness of biogas production from biomass is limited by the presence of polymeric structures, which are recalcitrant to digestion by bacteria. Therefore, pretreatments must often be applied prior to anaerobic fermentation to increase yields of biogas. Many physico-chemical pretreatments have a high energy demand and are generally costly. An alternative could be the ignition of a plasma directly in the biomass substrate. The reactive species that are generated by plasma-liquid interactions, such as hydroxyl radicals and hydrogen peroxides, could contribute significantly to the disintegration of cell walls and the breakage of poorly digestible polymers. With respect to economic, processing, and other potential benefits, a microwave instigated and sustained plasma was investigated. A microwave circuit transmitted 2-kW pulses into a recirculated sodium carboxymethyl cellulose solution, which mimicked the rheological properties of biomass. Each microwave pulse had a duration of 12.5 ms and caused the ignition of a discharge after a vapor bubble had formed. Microwaves were absorbed in the process with an efficiency of ∼97%. Slow-motion imaging showed the development of the discharge. The plasma discharges provoked a decrease in the viscosity, probably caused by the shortening of polymer chains of the cellulose derivative. The decrease in viscosity by itself could reduce processing costs and promotes bacterial activity in actual biomass. The results demonstrate the potential of microwave in-liquid plasma discharges for the pretreatment of biomass. © 2020 Author(s).
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    The equivalent circuit approach for the electrical diagnostics of dielectric barrier discharges: The classical theory and recent developments
    (Basel : MDPI AG, 2019) Pipa, Andrei V.; Brandenburg, Ronny
    Measurements of current and voltage are the basic diagnostics for electrical discharges. However, in the case of dielectric barrier discharges (DBDs), the measured current and voltage waveforms are influenced by the discharge reactor geometry, and thus, interpretation of measured quantities is required to determine the discharge properties. This contribution presents the main stages of the development of electrical diagnostics of DBDs, which are based on lumped electrical elements. The compilation and revision of the contributions to the equivalent circuit approach are targeted to indicate: (1) the interconnection between the stage of development, (2) its applicability, and (3) the current state-of-the-art of this approach. © 2019 by the authors.
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    On the relationship between SiF4plasma species and sample properties in ultra low-k etching processes
    (New York, NY : American Inst. of Physics, 2020) Haase, Micha; Melzer, Marcel; Lang, Norbert; Ecke, Ramona; Zimmermann, Sven; van Helden, Jean-Pierre H.; Schulz, Stefan E.
    The temporal behavior of the molecular etching product SiF4 in fluorocarbon-based plasmas used for the dry etching of ultra low-k (ULK) materials has been brought into connection with the polymer deposition on the surface during plasma treatment within the scope of this work. For this purpose, time-resolved measurements of the density of SiF4 have been performed by quantum cascade laser absorption spectroscopy. A quantification of the non-linear time dependence was achieved by its characterization via a time constant of the decreasing SiF4 density over the process time. The time constant predicts how fast the stationary SiF4 density is reached. The higher the time constant is, the thicker the polymer film on top of the treated ultra low-k surface. A correlation between the time constant and the ULK damage was also found. ULK damage and polymer deposition were proven by Variable Angle Spectroscopic Ellipsometry and X-ray Photoelectron Spectroscopy. In summary, the observed decay of the etching product concentration over process time is caused by the suppressed desorption of the SiF4 molecules due to a more dominant adsorption of polymers. © 2020 Author(s).
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    Does the energy transfer from Ar(1s) atoms to N2 lead to dissociation?
    (Hoboken, NJ : Wiley Interscience, 2020) Klages, Claus‐Peter; Martinovs, Andris; Bröcker, Lars; Loffhagen, Detlef
    Dielectric-barrier discharges (DBDs) in Ar–N2 mixtures, with N2 fractions in 0.1–1% range, would be attractive alternatives to DBDs in pure N2 if energy-transfer reactions between Ar(1s) atoms and N2 molecules were an efficient source of N atoms. Attempts to functionalize polyolefins in flowing postdischarges fed by such DBDs, as well as the search for the First Positive System in the emission spectrum, however, failed. Evidently, the energy-transfer reactions do not produce N atoms. For Ar(1s3) and Ar(1s5) metastable states, this fact has already been reported in the literature. For Ar(1s2) and Ar(1s4) resonant states, a quantitative argument is derived in this paper: energy transfer from Ar(1s) atoms to N2 molecules is not an efficient source of N atoms.
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    Plasma medical oncology: Immunological interpretation of head and neck squamous cell carcinoma
    (Hoboken, NJ : Wiley Interscience, 2020) Witzke, Katharina; Seebauer, Christian; Jesse, Katja; Kwiatek, Elisa; Berner, Julia; Semmler, Marie‐Luise; Boeckmann, Lars; Emmert, Steffen; Weltmann, Klaus‐Dieter; Metelmann, Hans‐Robert; Bekeschus, Sander
    The prognosis of patients suffering from advanced-stage head and neck squamous cell carcinoma (HNSCC) remains poor. Medical gas plasma therapy receives growing attention as a novel anticancer modality. Our recent prospective observational study on HNSCC patients suffering from contaminated tumor ulcerations without lasting remission after first-line anticancer therapy showed remarkable efficacy of gas plasma treatment, with the ulcerated tumor surface decreasing by up to 80%. However, tumor growth relapsed, and this biphasic response may be a consequence of immunological and molecular changes in the tumor microenvironment that could be caused by (a) immunosuppression, (b) tumor cell adaption, (c) loss of microbe-induced immunostimulation, and/or (d) stromal cell adaption. These considerations may be vital for the design of clinical plasma trials in the future.
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    Efficiency of plasma-processed air for biological decontamination of crop seeds on the premise of unimpaired seed germination
    (Hoboken, NJ : Wiley Interscience, 2021) Wannicke, Nicola; Wagner, Robert; Stachowiak, Joerg; Nishime, Thalita M.C.; Ehlbeck, Joerg; Weltmann, Klaus‐Dieter; Brust, Henrike
    In this study, the antimicrobial effect of plasma-processed air (PPA) generated by a microwave-induced nonthermal plasma was investigated for preharvest utilization using three crop species: Barley, rape, and lupine. Bacillus atrophaeus spores were chosen as a model, inoculated onto seeds, and subsequently treated with PPA at two different flow rates, different filling regimes, and gas exposure times. PPA treatment was efficient in reducing viable spores of B. atrophaeus, reaching sporicidal effects in all species at certain parameter combinations. Maximum germination of seeds was strongly reduced in barley and rape seeds at some parameter combination, whereas it had a modest effect on lupine seeds. Seed hydrophilicity was not altered. Overall, PPA investigated in this study proved suitable for preharvest applications.
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    HelixJet: An innovative plasma source for next-generation additive manufacturing (3D printing)
    (Hoboken, NJ : Wiley Interscience, 2020) Schäfer, Jan; Quade, Antje; Abrams, Kerry J.; Sigeneger, Florian; Becker, Markus M.; Majewski, Candice; Rodenburg, Cornelia
    A novel plasma source (HelixJet) for use in additive manufacturing (AM)/3D printing is proposed. The HelixJet is a capacitively coupled radio frequency plasma with a double-helix electrode configuration that generates a surprisingly stable and homogeneous glow plasma at low flow rates of argon and its mixtures at atmospheric pressure. The HelixJet was tested on three polyamide powders usually used to produce parts by laser sintering, a powder-based AM process, to form local deposits. The chemical composition of such plasma-printed samples is compared with thermally produced and laser-sintered samples with respect to differences in morphology that result from the different thermal cycles on several length scales. Plasma prints exhibit unique features attributable to the nonequilibrium chemistry and to the high-speed heat exchange.
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    Effect of cold atmospheric pressure plasma treatment of eggshells on the total bacterial count inoculated Salmonella Enteritidis and selected quality parameters
    (Hoboken, NJ : Wiley Interscience, 2021) Moritz, Maike; Wiacek, Claudia; Weihe, Thomas; Ehlbeck, Jörg; Weltmann, Klaus‐Dieter; Braun, Peggy G.
    In the European Union, foodborne outbreaks caused by Salmonella Enteritidis, related to eggs and egg products, have even been reported in 2018. Atmospheric pressure plasma is becoming increasingly important as a decontamination method. A semidirect cold atmospheric pressure plasma, the flexible electrode plasma source, was developed for treating whole hen's eggs. An average reduction of 1.16 and 0.95 log colony-forming units (CFU)/egg was achieved for the total bacterial count of clean and dirty eggs, respectively. An inactivation of 4.1 log CFU/egg Salmonella Enteritidis was achieved with artificially inoculated eggshells. Selected quality parameters and sensory properties were analysed. Overall, the present study yielded promising results for a realistic implementation of an industrial prototype plasma source.
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    White paper on plasma for medicine and hygiene: Future in plasma health sciences
    (Hoboken, NJ : Wiley Interscience, 2019) Bekeschus, Sander; Favia, Pietro; Robert, Eric; von Woedtke, Thomas
    Plasma Science and Technology offer their valuable contribution to human health since more than 50 years, after decades of experiences in the field of biomaterials; and more than a decade in using plasmas for therapeutic uses in medicine. Current knowledge as well as key challenges and opportunities for the human health have been intensely discussed during the Future in Plasma Science II (FIPS II) workshop in February 2016 in Greifswald, Germany. This contribution summarizes the major outcomes of the meeting and the current literature and consensus with an emphasis on major challenges in the fields of Plasma Science and Technology for improving human health.
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    Inactivation of airborne bacteria by plasma treatment and ionic wind for indoor air cleaning
    (Hoboken, NJ : Wiley Interscience, 2020) Prehn, Franziska; Timmermann, Eric; Kettlitz, Manfred; Schaufler, Katharina; Günther, Sebastian; Hahn, Veronika
    Airborne bacteria are a general problem in medical or health care facilities with a high risk for nosocomial infections. Rooms with a continuous airflow, such as operation theaters, are of particular importance due to a possible dissemination and circulation of pathogens including multidrug-resistant microorganisms. In this regard, a cold atmospheric-pressure plasma (CAP) may be a possibility to support usual disinfection procedures due to its decontaminating properties. The aim of this study was to determine the antimicrobial efficacy of a plasma decontamination module that included a dielectric barrier discharge for plasma generation. Experimental parameters such as an airflow velocity of 4.5 m/s and microbial contaminations of approximately 6,000 colony-forming units (cfu)/m3 were used to simulate practical conditions of a ventilation system in an operating theater. The apathogenic microorganism Escherichia coli K12 DSM 11250/NCTC 10538 and the multidrug-resistant strains E. coli 21181 and 21182 (isolated from patients) were tested to determine the antimicrobial efficacy. In summary, the number of cfu was reduced by 31–89% for the tested E. coli strains, whereby E. coli K12 was the most susceptible strain toward inactivation by the designed plasma module. A possible correlation between the number or kind of resistances and susceptibility against plasma was discussed. The inactivation of microorganisms was affected by plasma intensity and size of the plasma treatment area. In addition, the differences of the antimicrobial efficacies caused through the nebulization of microorganisms in front (upstream) or behind (downstream) the plasma source were compared. The presence of ionic wind had no influence on the reduction of the number of cfu for E. coli K12, as the airflow velocity was too high for a successful precipitation, which would be a prerequisite for an increased antimicrobial efficacy. The inactivation of the tested microorganisms confirms the potential of CAP for the improvement of air quality. The scale-up of this model system may provide a novel tool for an effective air cleaning process.