Inactivation of coronaviruses under irradiation by UVA-range light-emitting diodes

We report the results of the development of an experimental stand based on UVA light-emitting diodes (UVA LEDs) with radiation wavelengths of 385 and 395 nm for studying experimentally the inactivation of viruses of the coronavirus family, including SARS-CoV-2. Methodological grounds are presented for determining the inactivation dose that provides a predetermined decrease in the virus titre under the impact of UVA radiation. The effect of the diode radiation divergence on the virus photoinactivation process is investigated. It is shown that UVA LEDs can be used to reduce the virus titre by 4 orders of magnitude.

Исследование пространственных характеристик излучения квантовых каскадных лазеров для спектрального диапазона 8 μm

The near and far fields of quantum cascade lasers emitting in the spectral range near 8 µm have been studied. Lasing in the fundamental waveguide mode along the "fast" axis with a divergence of ~ 50º was observed in all samples of lasers with stripe widths of 22 and 50 µm in the entire range of pump currents. On the "slow" axis, multimode lasing and competition between the fundamental and higher waveguide modes were observed, which manifests itself for lasers with a 50 µm stripe in an increase of the radiation divergence from ~ 10º near the threshold to > 50º with a two-fold excess of the lasing threshold. The divergence along the slow axis for lasers with a stripe width of 22 µm remained unchanged over the entire range of pump currents and amounted to ~ 50º. The significant contribution of the fundamental mode to the total radiation intensity of quantum cascade lasers, being obvious from the far-field intensity distribution, cannot be established solely from the results of measurements of the near-field.

A Nonaxisymmetric Solution of Einstein’s Equations Featuring Pure Radiation from a Rotating Source

A special nonaxisymmetric solution of Einstein’s equations is derived, representing pure radiation from a rotating isolated source. The spacetime is assumed to be algebraically special having a multiple null eigenvector of the Weyl tensor forming a geodesic, shear-free, diverging, and twisting congruence k. Employing a complex null tetrad involving the vector k, the Ricci tensor, density of the radiation, divergence, and twist are calculated for the derived metric. A particular (nonaxisymmetric) subcase is shown to be flat at infinity and to contain the axisymmetric radiating Kerr metric, derived by Kramer and separately by Vaidya and Patel, as a special case. The spacetime is of Petrov type II and without Killing vectors.