Satellite Measurements of Plasma Disturbances and Electric Currents Induced in the Midlatitude Ionosphere Modified by High-Power HF Radio Waves

Abstract: We have analyzed the experimental data obtained in 2016–2019 from the measurements of plasma disturbances and electric currents induced at ionospheric altitudes upon the modification of the F2 region of the midlatitude ionosphere by means of high-power HF radio waves emitted by the SURA heating facility. The measurements were carried out using the onboard instruments of the SWARM satellites. The conditions for the generation of electric currents and the dependence of their characteristics on the ionospheric conditions were determined. The satellite measurement results were compared with the results of experiments in laboratory plasma. The development of artificial plasma disturbances in the Earth’s outer ionosphere was found to depend on thermal diffusion processes with unipolar diffusion coefficients, which are accompanied by the excitation of short-circuit eddy currents in the background plasma

Precipitation of Energetic Electrons from the Earth’s Radiation Belt Stimulated by High-Power HF Radio Waves for Modification of the Midlatitude Ionosphere

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Based on the results of the experiments performed in 2005–2010 within the framework of the Sura—DEMETER program, we analyze the features of the precipitations of energetic electrons (with energies E ≈ 100 keV) from the Earth’s radiation belt. The modification of the ionospheric F2 region was conducted by means of high-power HF O-mode radio waves radiated in the CW regime. The precipitations were detected using the equipment onboard DEMETER, a French microsatellite. The conditions of precipitation appearance were determined, and it was found that the electron precipitation region was stretched along the geomagnetic meridian to a distance of 1300 km; the size of the region in the transverse direction is about 400 km. It was shown by ionosonde measurements that such precipitations lead to increased absorption of radio waves in the lower ionosphere. It is assumed that the mechanism for precipitation of electrons from the Earth’s radiation belt is determined by the interaction of energetic electrons with VLF radio waves, which are generated due to the interaction of the amplitude-unmodulated O-mode pump wave with the ionospheric plasma near the wave reflection height

The photophysical and metal coordination properties of the N-CH3 substituted porphyrins: H(N-CH3)TPP vs H(CH3)OEP

The effect of N-methyl substitution on photophysical and metal coordination properties of the respective derivatives of octaethylporphyrin (H2OEP) and tetraphenylporphyrin (H2TPP) was studied by means of steady-state and time-resolved optical spectroscopies combined with semi-empirical quantum-chemical calculations and coordination chemistry methods. In case of H2TPP, the insertion of the methyl substituent into the center of the porphyrin macrocycle leads to noticeable nonplanar distortions of the molecule and is accompanied by changes of its photophysical and physicochemical properties towards those manifested by "classical" nonplanar porphyrins. Contrasting to that, N-methyl substituted H2OEP does not undergo significant nonplanar distortions and possesses photophysical characteristics mainly similar to unsubstituted H2OEP, except for the long-wavelength shift of the absorption and emission bands. The Zn coordination/Zn complex dissociation and macrocycle thermal stability parameters were also determined for both N-methyl substituted and parent unsubstituted macrocycles, which correlate well with a higher degree of nonplanarity of the N-methyl substituted H2TPP as compared to H2OEP. Basing on the results of this study the conclusion postulated is that N-methyl substitution has a different effect on the photophysical and coordination properties of H2TPP vs. H2OER Copyright (c) 2005 Society of Porphyrins & Phthalocyanines

The yeast counterparts of human 'MELAS' mutations cause mitochondrial dysfunction that can be rescued by overexpression of the mitochondrial translation factor EF-Tu

We have taken advantage of the similarity between human and yeast (Saccharomyces cerevisiae) mitochondrial tRNA(Leu)(UUR), and of the possibility of transforming yeast mitochondria, to construct yeast mitochondrial mutations in the gene encoding tRNA(Leu)(UUR) equivalent to the human A3243G, C3256T and T3291C mutations that have been found in patients with the neurodegenerative disease MELAS (for mitochondrial 'myopathy, encephalopathy, lactic acidosis and stroke-like episodes'). The resulting yeast cells (bearing the equivalent mutations A14G, C26T and T69C) were defective for growth on respiratory substrates, exhibited an abnormal mitochondrial morphology, and accumulated mitochondrial DNA deletions at a very high rate, a trait characteristic of severe mitochondrial defects in protein synthesis. This effect was specific at least in the pathogenic mutation T69C, because when we introduced A or G instead of C, the respiratory defect was absent or very mild. All defective phenotypes returned to normal when the mutant cells were transformed by multicopy plasmids carrying the gene encoding the mitochondrial elongation factor EF-Tu. The ability to create and analyse such mutated strains and to select correcting genes should make yeast a good model for the study of tRNAs and their interacting partners and a practical tool for the study of pathological mutations and of tRNA sequence polymorphisms