Ms. Elizaveta Yu. Letova Profile

Elizaveta Yu. Letova

at ITMO Univ.

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Proceedings Article | 11 December 2019 Paper

Features of the formation of barrier discharge in xenon excimer lamps

Galina Zvereva, Elizaveta Yu. Letova

Proceedings Volume 11322, 1132222 (2019) https://doi.org/10.1117/12.2548856

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The features of the formation of a barrier discharge in xenon (p = 300 Torr) depending on the frequency of the pulses of the applied voltage were studied in this work. It was found that the discharge in the frequency range f = 1–40 kHz has three modes: 1) visually homogeneous low-power mode at f = 1–4 kHz, 2) channel mode at f≈5 kHz, and uniform powerful one at f> 5 kHz. Dependences of current and voltage on time indicate that at f ≤5 kHz the discharge is initiated due to streamer and at f> 5 kHz due to the Townsend breakdown mechanisms. The transition from a low-power to a channel mode can be explained by thermal constriction: the gas temperature gradient and spatial heterogeneity of the electron production increase with frequency growth, aggravated by the death of electrons during dissociative recombination. The transition from a channel mode to a homogeneous powerful one can be explained by an increase in stepwise ionization, which reduces the spatial inhomogeneity of electron production. In argon and krypton discharges of a similar design in the frequency range f = 1–40 kHz, only a uniform powerful mode, initiated by the Townsend breakdown mechanism, was observed. This can be explained by lower values of the dissociative recombination rates in Ar and Kr in comparison with Xe and larger values of electron diffusion coefficients. In the VUV emission spectrum of the Xe discharge a band was observed with a maximum at λ= 173 nm. The intensity of the band linearly increased from 1 to 30 mW/cm² in the range f = 1–40 kHz. In the UV region a low intensity continuum with a maximum at λ = 270 nm was observed. In the visible region, Xe atomic lines were recorded in the area λ = 440-500 nm, which appear as a result of dissociative recombination of the Xe₂⁺ ion.

Proceedings Article | 11 December 2019 Paper

Indirect action of VUV radiation on micro-organisms

Galina Zvereva, Irina Yu. Kirtsidely, Eduard Machs, Elizaveta Yu. Letova

Proceedings Volume 11322, 113222M (2019) https://doi.org/10.1117/12.2548657

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The contribution of the indirect mechanism to the inactivation of microorganisms by long wavelength VUV radiation (λ>170 nm) was investigated in this work. For these purposes dry spores of microscopic fungi Rhodotorula colostri and Saccharomyces cerevisiae were irradiated by Xe excilamp (λ= 173 nm).To determine the contribution of indirect action to the microfungi inactivation, the survival probabilities of the samples grown on a nutrient medium containing antioxidant (I₂) and without it were carried out. The results have shown, that the survival probabilities of the spores containing antioxidant increases by no less than 20-25% compared to control ones. The increase value depends on VUV irradiation dose and microorganism type. It should be emphasized, that due to the masking of microfungi survival by I₂ bactericidal action, the obtained survival probability increase values should be considered as a lower estimate. Electrophoresis of microfungi DNA have shown, that VUV irradiation of spores containing antioxidants leads to less DNA destruction and heaver DNA fragments appearance. The latter may indicate a decrease of reactive oxygen species effect on DNA in the presence of antioxidants. Atomic force microscopy and IR spectroscopy haven’t shown influence of antioxidant on cell wall destruction. This can indicate, that in contrast to wet spores, in the case of VUV irradiation of dry ones, the indirect mechanism of cell wall destruction is absent or weakly expressed.

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