Haggag S., Ramadan M. «Applications of optimal control to general relativity» Нелинейный мир, 22, № 3, с. 35-48 (2024)

Two classes of applications of optimal control to problems in General Relativity are reviewed. The first class includes direct applications where each problem has beforehand a specific objective function. Two examples of this class are reviewed, where optimal control leads directly to the optimal solutions. Results show that optimal control is more powerful than classical variational calculus. The second class includes innovative applications where problems in General Relativity may be approached by introducing appropriate objective functions. Three examples of this class are reviewed, where an optimal inflationary universe, an optimal cosmological model and an optimal stellar model are, respectively, constructed. Results show that optimal control adds physical significance to solutions of such problems.

Li N., He X.P., Yuan Y. «Research of a Stepped Ultrasonic Radiator» Акустический журнал, 71, № 3, с. pp312-325 (2025)

Sound field and radiation impedance are crucial acoustic performance parameters. Sound field calculation concerns sound propagation from a source and pertains to practical application problems within a specific environment. In contrast, radiation impedance is associated with the matching of the radiating elements with a circuit. Free boundary stepped radiators with high directional properties have significant application potential in the field of high-power gas medium ultrasonics. This study proposes a simulation for the computational estimation of the radiation field and impedance of stepped radiators based on the Rayleigh method. The axial sound pressure and directivity of the rectangular stepped radiator are calculated theoretically. At the same time, the radiation impedance is calculated. The results of the sound field test and radiation impedance calculations verified the validity of the proposed method. Thus, a practical and efficient approach to the analysis of the acoustic performance of arbitrary sound radiator was realized. The proposed method offers valuable insights and addresses a crucial gap in understanding these parameters for diverse radiator configurations.

Huang L., Zeng R. «Geometry-Dependent Performance in Sound Localization: A Study of 18-Element Microphone Arrays» Акустический журнал, 71, № 2, с. pp135-143 (2025)

This study examines the performance of six different two-dimensional, 18-element microphone array geometries–BK, Ring, Reuleaux, Logarithmic, Triangle, and Starfish–for sound source localization. The arrays’ performances are systematically evaluated using beamforming algorithms and acoustic pressure reconstruction, focusing on key metrics such as main lobe width, side lobe magnitude, reconstruction error, and resolution quality over frequencies ranging from 0 to 3000 Hz. Additionally, the study investigates the adaptability of these configurations at various distances and explores their frequency-dependent behavior. The results indicate that array geometry substantially impacts localization accuracy, with the Starfish configuration demonstrating superior overall performance, exhibiting the narrowest main lobe width, highest main lobe amplitude, lowest reconstruction error, and consistently high resolution. Thus, the Starfish configuration is recommended as optimal for effective sound source localization applications.