Synthesis of 3‐(5‐Methylthiophen‐2‐yl)coumarins and Their Photochromic Dihetarylethene Derivatives

Novel unsymmetrical di(thienyl)maleic acid anhydride, including coumarin moiety, has been designed and synthesized. Its photochromism study and fatigue resistance estimation are reported. Microwave‐assisted procedure has been successfully used for synthesis of 3‐(5‐methylthiophen‐2‐yl)coumarins.     

Mechanism of generation of runaway electrons in a lightning leader

A mechanism is analyzed of the electric field enhancement in a lightning leader up to the level permitting runaway of low-energy electrons. The ionization wave propagation in the preionized domain in front of the leader makes it possible to overcome the limitation imposed on the field intensity by transversal expansion of the leader front. By means of numerical simulations, it is demonstrated that, at the final stage of formation of a new leader step, generation of an electric field is possible in the channels of the streamer zone ahead of the new step with intensity sufficient for electron runaway and, consequently, for producing the X-ray and γ-ray pulses observed in correlation with the lightning leader steps.     

Lightning initiation mechanism based on the development of relativistic runaway electron avalanches triggered by background cosmic radiation: Numerical simulation

The mechanism of lightning initiation due to electric field enhancement by the polarization of a conducting channel produced by relativistic runaway electron avalanches triggered by background cosmic radiation has been simulated numerically. It is shown that the fields at which the start of a lightning leader is possible even in the absence of precipitations are locally realized for realistic thundercloud configurations and charges. The computational results agree with the in-situ observations of penetrating radiation enhancement in thunderclouds.     

Investigation of prebreakdown currents flowing in pseudospark gaps

Currents flowing at the prebreakdown stage in a pseudospark-gap switch with an ignition unit based a steady-state glow discharge are studied. The mechanism of operation of the blocking electrodes is explained. An electrode construction that makes it possible to increase substantially the static breakdown voltage of the device is presented. Zh. Tekh. Fiz. 67, 26–29 (October 1997)     

Source of a Mega-Ampere Current with ~100-ns Time of Rise Based on an Explosive Magnetic Generator

Doklady Physics - To achieve the thermonuclear-ignition threshold in the scheme of indirect X-ray irradiation of the Z-pinch, it is necessary to implode the liner by a current with an amplitude of...     

Fluorescence excited in a thunderstorm atmosphere by relativistic runaway electron avalanches

The spectrum and spatiotemporal evolution of the fluorescence of an atmospheric discharge developing in the regime of relativistic runaway electron avalanche (RREA) generation have been calculated without involving the relativistic feedback. The discharges generating narrow bipolar pulses, along with the discharges responsible for terrestrial gamma-ray flashes, are shown to be relatively dark. Nevertheless, the fluorescence excited by a discharge involving RREAs can be recorded with cameras used to record high-altitude optical phenomena. A possible connection between a certain class of optical phenomena observed at the tops of thunderclouds and RREA emission is pointed out.     

Synthesis and photoinduced fluorescence of 3-(2-hetarylethenyl)chromen-2-ones

3-(2-Hetarylethenyl)chromen-2-ones were synthesized for the first time, following two different schemes, and their spectral and photochemical properties were studied. The title compounds were found to undergo both reversible and irreversible photoinduced transformations which are accompanied by considerable change of the fluorescence pattern.