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.

Yicen Li, Rongguang Li, Ling Sun, Chen Sixun Sun, Zhiqiang Cheng «Stress Measurement of Orthogonal Fiber-Reinforced Composites under Biaxial Stress Conditions Based on Critically Refracted Longitudinal Wave Method» Акустический журнал, 71, № 3, с. pp368-377 (2025)

This study derives the relationship between ultrasonic velocity and stress in orthogonal fiber-reinforced composites under biaxial stress conditions. By calibrating the stress coefficients in two directions, the stress values in the composite plate can be obtained using two time-of-flight measurements. The calibration of stress coefficients requires determining the first critical incident angle. Thus, micromechanics methods were used to calculate the stiffness matrix of the composite material, which was then input into a finite element model to simulate the ultrasonic velocity in the orthogonal composite material. This process determined the incident angle capable of exciting the critical refracted longitudinal wave, namely the first critical incident angle. Rectangular specimens of orthogonal composites were manufactured from glass fiber-reinforced composite plates with bidirectional layup, and uniaxial tensile tests were conducted to verify the accuracy of the first critical incident angle and to calibrate the stress coefficients. It was found that the normal stress in the fiber direction results in a decrease in the ultrasonic velocity in both the fiber and perpendicular directions. To verify the accuracy of ultrasonic stress measurement, uniaxial tensile specimens with a central hexagonal area under biaxial stress conditions and standard biaxial tensile specimens were specially designed. The experimental results for both specimens showed that the ultrasonic stress measurement results were in good agreement with the stress measured using strain gauges, confirming the accuracy and practicality of the ultrasonic stress measurement method.

Kravchenko E.A., Rubtsov G.I., Zhadan D.S. «Towards Baikal-Top: Feasibility Study of an Onshore Detector System for the Joint Registration of EAS with Baikal-GVD» Журнал экспериментальной и теоретической физики, 169, № 2, с. 205-211 (2026)

We study the possibility of registering high-energy extensive air showers (EAS) by the onshore detector facility simultaneously with the trigger of the Baikal-GVD neutrino telescope. The location of the surface detector array on the shore of Lake Baikal is motivated by the fact that permanent placement of detectors on the surface of the lake is challenging. Within the given geometry, simultaneous registration is possible for EAS with a zenith angle of about 76 degrees within the limited solid angle. The corresponding inclined EAS are dominated by muons and significantly attenuated. The installation will make it possible to obtain an estimate of the number of high-energy muons in EAS. This, subsequently, would make it possible to verify EAS modeling and calculations of the atmospheric neutrino flux. The detector may also be used for cross-calibration of energy and direction measurements by the neutrino telescope. We use the CORSIKA program to simulate the registration of EAS on the shore close to the Baikal-GVD. The propagation of ultra-high energy muons produced by EAS through 3.5 km of water and their registration by Baikal-GVD is simulated using the PROPOSAL package. We calculate the minimal total area of the onshore detectors suitable for several cosmic ray energy thresholds, starting from 1 PeV. The report presents estimates of the number of events jointly registered by the onshore installation and the Baikal-GVD the EAS registration detector systems with different areas. Keywords: ultra-high-energy cosmic rays, extensive air showers, Baikal-GVD, Baikal-Top, muon puzzle, high energy muons