M. D. Dolberg, N. N. Iasnitzkaia. Estimation from below of oscillation frequencies of elastic systems . . . 507

I. L. Kantor, A. I. Sirota, A. S. Solodovnikov. A class of symmetric spaces with an extensible group of motion and a generalization of Poincaré model . . . 511

R. I. Kachurovskii. Non-linear equations with monotonic operators and with some other ones . . . 515

A. M. Molchanov. Uniform asymptotic of linear systems . . . 519

S. I. Nedev. Symmetrizable spaces and ε-mappings . . . 523

S. I. Serdiukova. The necessary and sufficient condition for stability in a uniform metric of difference equation systems . . . 526

G. N. Tiurina. A type of contractible curves . . . 529

CYBERNETICS AND THE REGULATION THEORY

G. M. Adelson-Velskii, P. E. Kunin, A. A. Leman. A class of learning recognition algorithms . . . 532

N. N. Krasovskii. On the game-type rendes-vous of motions . . . 535

PHYSICS

N. G. Basov, V. A. Boiko, O. N. Krokhin, G. N. Sklizkov. The formation of a long spark in the air induced by slightly focussed laser radiation . . . 538

O. N. Voronko, N. A. Kozlov, A. A. Mak, B. G. Malinin, A. I. Stepanov. On a possibility of increasing the quality factor of the resonator in the neodymium optical quantum generator . . . 542

G. E. Gernet. The variation of angular and energy distribution of charged particles in a flow when crossing a magnetic field . . . 544

V. A. Moskalenko. The electrodynamics of bizonal superconductors. The neighbourhood of the upper critical field . . . 546

A. V. Shelest. Irreversible evolution of a dynamic system interacting with a statistic ensemble . . . 550

TECHNICAL PHYSICS

N. E. Alexeevskii, I. I. Kornilov, N. M. Matveeva, Iu. A. Maximov. Superconductivity in the Nb₃Al — Mo₃Al system . . . 553

N. L. Kafengauz. Features of heat transfer to a turbulent flow of liquid at supercritical pressure . . . 557

G. I. Nosova, N. T. Travina. The dependence of the critical shearing stress upon the temperature in copper — nickel — cobalt alloys . . . 560

E. S. Filippov, V. K. Grigorovich, A. M. Samarin. Structural transition in iron — carbon melts . . . 564

GEOPHYSICS

P. S. Gasiukov, N. P. Smirnov. Pressure field oscillations over the northern hemisphere within the eleven-year cycle of solar activity . . . 567

CRYSTALLOGRAPHY

Iu. G. Asadov. Growth of a hexagonal selenium crystal from a single monoclinic selenium crystal in polymorphic transformation . . . 570

A. V. Warshavskij, Iu. F. Shulpiakov. Oriented crystallization of α-SiC on diamond . . . 573

LETTER TO THE EDITOR

In our article (R. L. Sorochenko, E. V. Borodzich, “Detection in the Nebula NGC 6618 (Omega) of Radio Emission from a Line of Excited Hydrogen”), published in Doklady Akademii Nauk, vol. 163, no. 3, 1966, the stated value of the brightening of the nebula at the line frequency, \((4.2 \mp 1.9)\%\), was determined without a correction for the coefficient that takes into account the effect of the analyzer band on the line intensity.

Taking this coefficient into account, the brightening of the nebula NGC 6618 at the line frequency is \((6.8 \mp 1.9)\%\).

R. L. Sorochenko E. V. Borodzich