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- ItemNonenzymatic post-translational modifications in peptides by cold plasma-derived reactive oxygen and nitrogen species(Melville, NY : AIP, 2020) Wenske, Sebastian; Lackmann, Jan-Wilm; Bekeschus, Sander; Weltmann, Klaus-Dieter; Von Woedtke, Thomas; Wende, KristianCold physical plasmas are emerging tools for wound care and cancer control that deliver reactive oxygen species (ROS) and nitrogen species (RNS). Alongside direct effects on cellular signaling processes, covalent modification of biomolecules may contribute to the observed physiological consequences. The potential of ROS/RNS generated by two different plasma sources (kINPen and COST-Jet) to introduce post-translational modifications (PTMs) in the peptides angiotensin and bradykinin was explored. While the peptide backbone was kept intact, a significant introduction of oxidative PTMs was observed. The modifications cluster at aromatic (tyrosine, histidine, and phenylalanine) and neutral amino acids (isoleucine and proline) with the introduction of one, two, or three oxygen atoms, ring cleavages of histidine and tryptophan, and nitration/nitrosylation predominantly observed. Alkaline and acidic amino acid (arginine and aspartic acid) residues showed a high resilience, indicating that local charges and the chemical environment at large modulate the attack of the electron-rich ROS/RNS. Previously published simulations, which include only OH radicals as ROS, do not match the experimental results in full, suggesting the contribution of other short-lived species, i.e., atomic oxygen, singlet oxygen, and peroxynitrite. The observed PTMs are relevant for the biological activity of peptides and proteins, changing polarity, folding, and function. In conclusion, it can be assumed that an introduction of covalent oxidative modifications at the amino acid chain level occurs during a plasma treatment. The introduced changes, in part, mimic naturally occurring patterns that can be interpreted by the cell, and subsequently, these PTMs allow for prolonged secondary effects on cell physiology. © 2020 Author(s).
- ItemData processing techniques for ion and electron-energy distribution functions(Melville, NY : AIP, 2023) Caldarelli, A.; Filleul, F.; Boswell, R. W.; Charles, C.; Rattenbury, N. J.; Cater, J. E.Retarding field energy analyzers and Langmuir probes are routinely used to obtain ion and electron-energy distribution functions (IEDF and EEDF). These typically require knowledge of the first and second derivatives of the current-voltage characteristics, both of which can be obtained using analog and numerical techniques. A frequent problem with electric-probe plasma diagnostics is the noise from the plasma environment and measurement circuits. This poses challenges inherent to differentiating noisy signals, which often require prior filtering of the raw current-voltage data before evaluating the distribution functions. A review of commonly used filtering and differentiation techniques is presented. It covers analog differentiator circuits, polynomial fitting (Savitzky-Golay filter and B-spline fitting), window filtering (Gaussian and Blackman windows) methods as well as the AC superimposition and Gaussian deconvolution routines. The application of each method on experimental datasets with signal-to-noise ratios ranging from 44 to 66 dB is evaluated with regard to the dynamic range, energy resolution, and signal distortion of the obtained IEDF and EEDF as well as to the deduced plasma parameters.
- ItemPhysical regimes of electrostatic wave-wave nonlinear interactions generated by an electron beam propagating in a background plasma(Melville, NY : AIP, 2022) Sun, Haomin; Chen, Jian; Kaganovich, Igor D.; Khrabrov, Alexander; Sydorenko, DmytroElectron-beam plasma interaction has long been a topic of great interest. Despite the success of the quasilinear and weak turbulence theories, their validities are limited by the requirements of a sufficiently dense mode spectrum and a small wave amplitude. In this paper, we extensively study the collective processes of a mono-energetic electron beam emitted from a thermionic cathode propagating through a cold plasma by performing high-resolution two-dimensional particle-in-cell simulations and using analytical theories. We confirm that, during the initial stage of two-stream instability between the beam and background cold electrons, it is saturated due to the well-known wave-trapping mechanism. Further evolution occurs due to strong wave-wave nonlinear processes. We show that the beam-plasma interaction can be classified into four different physical regimes in the parameter space for the plasma and beam parameters. The differences between the regimes are analyzed in detail. We identify a new regime in the strong Langmuir turbulence featured by what we call electron modulational instability (EMI) that could create a local Langmuir wave packet growing faster than the ion plasma frequency. Ions do not have time to respond to EMI in the initial growing stage. On a longer timescale, the action of the ponderomotive force produces very strong ion density perturbations, and eventually, the beam-plasma wave interaction stops being resonant due to the strong ion density perturbations. Consequently, in this EMI regime, electron beam-plasma interaction occurs in a repetitive (intermittent) process. The beam electrons are strongly scattered by waves, and the Langmuir wave spectrum is significantly broadened, which in turn gives rise to strong heating of bulk electrons. Associated energy transfer from the beam to the background plasma electrons has been studied. A resulting kappa (κ) distribution and a wave-energy spectrum E2(k)∼k-5 are observed in the strong turbulent regime.
- ItemPhysics of e × B discharges relevant to plasma propulsion and similar technologies(Melville, NY : AIP, 2020) Kaganovich, Igor D.; Smolyakov, Andrei; Raitses, Yevgeny; Ahedo, Eduardo; Mikellides, Ioannis G.; Jorns, Benjamin; Taccogna, Francesco; Gueroult, Renaud; Tsikata, Sedina; Bourdon, Anne; Boeuf, Jean-Pierre; Keidar, Michael; Powis, Andrew Tasman; Merino, Mario; Cappelli, Mark; Hara, Kentaro; Carlsson, Johan A.; Fisch, Nathaniel J.; Chabert, Pascal; Schweigert, Irina; Lafleur, Trevor; Matyash, Konstantin; Khrabrov, Alexander V.; Boswell, Rod W.; Fruchtman, AmnonThis paper provides perspectives on recent progress in understanding the physics of devices in which the external magnetic field is applied perpendicular to the discharge current. This configuration generates a strong electric field that acts to accelerate ions. The many applications of this set up include generation of thrust for spacecraft propulsion and separation of species in plasma mass separation devices. These "E × B"plasmas are subject to plasma-wall interaction effects and to various micro- and macroinstabilities. In many devices we also observe the emergence of anomalous transport. This perspective presents the current understanding of the physics of these phenomena and state-of-the-art computational results, identifies critical questions, and suggests directions for future research.
- ItemProvenance information as a tool for addressing engineered nanoparticle reproducibility challenges(Melville, NY : AIP, 2016) Baer, Donald R.; Munusamy, Prabhakaran; Thrall, Brian D.Nanoparticles of various types are of increasing research and technological importance in biological and other applications. Difficulties in the production and delivery of nanoparticles with consistent and well defined properties appear in many forms and have a variety of causes. Among several issues are those associated with incomplete information about the history of particles involved in research studies, including the synthesis method, sample history after synthesis, including time and nature of storage, and the detailed nature of any sample processing or modification. In addition, the tendency of particles to change with time or environmental condition suggests that the time between analysis and application is important and some type of consistency or verification process can be important. The essential history of a set of particles can be identified as provenance information and tells the origin or source of a batch of nano-objects along with information related to handling and any changes that may have taken place since it was originated. A record of sample provenance information for a set of particles can play a useful role in identifying some of the sources and decreasing the extent of particle variability and the lack of reproducibility observed by many researchers.
- ItemReaction pathways of producing and losing particles in atmospheric pressure methane nanosecond pulsed needle-plane discharge plasma(Melville, NY : AIP, 2018) Zhao, Yuefeng; Wang, Chao; Li, Li; Wang, Lijuan; Pan, JieIn this work, a two-dimensional fluid model is built up to numerically investigate the reaction pathways of producing and losing particles in atmospheric pressure methane nanosecond pulsed needle-plane discharge plasma. The calculation results indicate that the electron collisions with CH4 are the key pathways to produce the neutral particles CH2 and CH as well as the charged particles e and CH3+. CH3, H2, H, C2H2, and C2H4 primarily result from the reactions between the neutral particles and CH4. The charge transfer reactions are the significant pathways to produce CH4+, C2H2+, and C2H4+. As to the neutral species CH and H and the charged species CH3+, the reactions between themselves and CH4 contribute to substantial losses of these particles. The ways responsible for losing CH3, H2, C2H2, and C2H4 are CH3 + H → CH4, H2 + CH → CH2 + H, CH4+ + C2H2 → C2H2+ + CH4, and CH4+ + C2H4 → C2H4+ + CH4, respectively. Both electrons and C2H4+ are consumed by the dissociative electron-ion recombination reactions. The essential reaction pathways of losing CH4+ and C2H2+ are the charge transfer reactions.
- ItemNumerical investigation of co-axial DBD: Influence of relative permittivity of the dielectric barrier, applied voltage amplitude, and frequency(Melville, NY : AIP, 2017) Gadkari, Siddharth; Gu, SaiIn this work, a one-dimensional numerical fluid model is developed for co-axial dielectric barrier discharge in pure helium and a parametric study is performed to systematically study the influence of relative permittivity of the dielectric barrier and the applied voltage amplitude and frequency on the discharge performance. Discharge current, gap voltage, and spatially averaged electron density profiles are presented as a function of relative permittivity and voltage parameters. For the geometry under consideration, both the applied voltage parameters are shown to increase the maximum amplitude of the discharge current peak up to a certain threshold value, above which it stabilized or decreased slowly. The spatially averaged electron density profiles follow a similar trend to the discharge current. Relative permittivity of the dielectric barrier is predicted to have a positive influence on the discharge current. At lower frequency, it is also shown to lead to a transition from Townsend to glow discharge mode. Spatially and time averaged power density is also calculated and is shown to increase with increasing relative permittivity, applied voltage amplitude, and frequency.
- ItemPreface: In focus issue on nanoparticle interfaces(Melville, NY : AIP, 2016) Ceccone, Giacomo; Shard, Alexander G.[no abstract available]