Reviews of topical problems

D.A. Trunin “Pedagogical introduction to the Sachdev—Ye—Kitaev model and two-dimensional dilaton gravity” Phys. Usp. 64 219–252 (2021)

A.D. Pogrebnyak, M.A. Lisovenko, A. Turlybekuly, V.V. Buranich “Protective coatings with nanoscale multilayer architecture: current state and main trends” Phys. Usp. 64 253–279 (2021)

V.P. Lukin “Outer scale of turbulence and its influence on fluctuations of optical waves” Phys. Usp. 64 280–303 (2021)

Instruments and methods of investigation

K.V. Zhukovsky “Undulator and free-electron laser radiation with field harmonics and off-axis effects taken into account analytically” Phys. Usp. 64 304–316 (2021)

Personalia

Yu.Yu. Balega, E.E. Boos, L.M. Zelenyi, V.V. Kalegaev, L.A. Kuzmichev, L.I. Miroshnichenko, A.A. Petrukovich, A.A. Petrukhin, V.V. Radchenko, V.I. Savrin, S.I. Svertilov, Yu.I. Stozhkov “In memory of Mikhail Igorevich Panasyuk” Phys. Usp. 64 317–318 (2021)

P.I. Arseev, A.A. Gorbatsevich, E.I. Demikhov, V.V. Kveder, N.N. Kolachevsky, Z.F. Krasil’nik, O.N. Krokhin, I.V. Kukushkin, G.A. Mesyats, R.A. Suris, V.B. Timofeev, I.A. Shcherbakov “In memory of Nikolai Nikolaevich Sibeldin” Phys. Usp. 64 319–320 (2021)

Physics news on the internet

Yu.N. Eroshenko “Physics news on the Internet (based on electronic preprints)” Phys. Usp. 64 321–323 (2021)