Covid-19 and Employment in Tourism: Challenges and Solutions

This article analyzes the impact of COVID-19 on tourism employment worldwide, and in particular in Uzbekistan. The article also presents some proposals to improve competitiveness and sustainability during the crisis

Bimetallic Ag-based catalysts for low-temperature SCR: Quo vadis?

The abatement of nitrogen oxides coming to the atmosphere from diesel engines of automotive vehicles and marine vessels, industrial plants, and other sources is of profound importance. Currently, catalysis-based solutions show growing potential in addressing this challenge. The main requirements that SCR catalysts should meet include enhanced low-temperature activity and selectivity combined with a broad operating window, high resistance to poisons and moisture. While a plethora of SCR catalysts has been proposed by now, recently, a growing number of publications have emphasized the unlocked potential of bimetallic catalyst formulations. Among them, Ag-based systems deserve special attention due to their high performance and relative cheapness. The present review is focused on the recent achievements recorded in the latest 5–10 years on bimetallic Agbased catalysts for low-temperature SCR. Systems, such as Ag-Pt, Ag-Au, Ag-Cu, Ag-Fe, Ag-Mn, are considered and compared with bi-and polymetallic transition metals. The role of catalysts preparation method, Ag loading, metal-support interaction and pre-treatment effects has been pointed out. The outlook of the future research challenges is provided

Photoluminescence frequency up-conversion in GaSe single crystals as studied by confocal microscopy

The photoluminescence spectrum of melt-grown GaSe single crystals was investigated with a confocal Raman microscope equipped with a HeNe laser. Three luminescence bands of different intensity were observed, which are mainly located to the blue of the laser line. The luminescence signals show a quadratic dependence on excitation intensity. The effect is interpreted as second-harmonic generation in the strongly optically nonlinear material followed by the excitation of electrons into the conduction band and luminescence emission from direct-gap Wannier excitons. The relative intensities of the three luminescence peaks exhibit a spatial variation on the crystal surface, which was mapped with the confocal microscope. Possible explanations of this effect are discussed. In an external electric field the luminescence shows a strong increase and a quadratic redshift, whose magnitude is consistent with the Franz-Keldysh mechanism. (C) 2002 American Institute of Physics