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Russian Scientists Have Discovered A New Physical Paradox

Russian Scientists Have Discovered A New Physical Paradox

Scientists of Peter the Great Saint Petersburg Polytechnic University (SPBPU) have discovered and theoretically explained a new physical effect, the essence of which is the possibility of increasing the amplitude of mechanical vibrations of an object without external influence. Besides, they suggested that if the paradox of Fermi-Pasta-Ulam-Scurvy.

SPBPU explained this using a simple example: to swing a swing, you need to constantly push it. It was believed that it was impossible to achieve vibrational resonance without constant external influence.

However, the scientific group of the Higher school of theoretical mechanics of the Institute of applied mathematics and mechanics of SPBPU has discovered a new physical phenomenon-ballistic resonance, in which mechanical vibrations can be excited solely at the expense of internal thermal resources of the system.

The key to understanding is the experimental work of scientific groups around the world, which showed that in ultra-pure crystalline materials at the nano-and micro-level, heat propagates at an abnormally high speed. This phenomenon is called ballistic thermal conductivity.

A scientific group led by a corresponding member of the Russian Academy of Sciences Anton Krivtsov has derived equations describing this phenomenon and made significant progress in understanding thermal processes at micro scales. In a study published in the scientific journal Physical Review E, scientists examined the behavior of systems at the initial periodic temperature distribution in a crystalline material.

The discovered phenomenon is that the process of heat equalization leads to the appearance of mechanical vibrations with increasing amplitude over time. The effect is called ballistic resonance.

"For the past few years, our research group has been investigating the mechanisms of heat propagation at the micro-and nanoscale levels. In the process, we found that at these levels, heat does not propagate in the way we expected — for example, heat can flow from cold to hot. This behavior of nanosystems leads to new physical effects, such as ballistic resonance," said Vitaly Kuzkin, associate Professor of the Higher school of theoretical mechanics at SPBPU. According to him, in the future, scientists want to understand how this can be used in such promising materials as graphene.

These discoveries also give the possibility of resolving the paradox of the Fermi-Pasta-Ulam-Scurvy. In 1953, a scientific group led by Enrico Fermi conducted what would become a famous computer experiment. Scientists have considered the simplest model of vibrations of a chain of particles connected by springs. It was assumed that the mechanical movement would gradually die down, turning into chaotic thermal vibrations, but the result was unexpected: the vibrations in the chain at first almost died out, but then revived and almost reached the initial level. The system returned to its initial state, and the cycle was repeated again. The reasons for the appearance of mechanical vibrations from the heat in the considered system have been the subject of scientific research and controversy for decades.

The amplitude of mechanical vibrations caused by ballistic resonance does not increase indefinitely but reaches a maximum, after which it begins to gradually decrease to zero. Over time, the mechanical vibrations fade completely, and the temperature equalizes along with the entire crystal. This process is called thermalization. For mechanics and physicists, this experiment is important because a chain of particles connected by springs is a good model of crystalline material.

Researchers of the Higher school of theoretical mechanics of SPBPU have shown that the transition of mechanical energy to heat is irreversible if we consider the process at finite temperature.

"It is usually not taken into account that in real materials, along with mechanical ones, there is thermal motion, the energy of which is several orders of magnitude higher. We recreated these conditions in a computer experiment and showed that it is the thermal motion that dampens the mechanical wave and prevents the revival of vibrations," explained Anton Krivtsov, Director of the Higher school of theoretical mechanics of SPBPU, corresponding member of the Russian Academy of Sciences.

According to experts, the theoretical approach proposed by SPBPU scientists allows us to take a new look at what is meant by heat and temperature and maybe of fundamental importance in the development of nanoelectronic devices of the future.