Vol 193, No 11 (2023)
Reviews of topical problems
Initial episodes of the chemical evolution of the intergalactic medium
Abstract
The current state of the problem of the origin and transport of ‘heavy’ ($A>4$) chemical elements in the Universe is discussed. The beginning of stellar nucleosynthesis (SNS) dates apparently to $z\gtrsim 20$ redshift epochs (age of the Universe $t_U\lesssim 180$ Myr). Presently, SNS traces are observed in some cases in galaxies at redshift $z\sim 10-15$ ($t_U\sim 500-270$ Myr). A massive redistribution of chemical elements from galaxies over the entire Universe became possible, primarily under the action of powerful explosions, in the reionization period at $z\lesssim 6$ {($t_U\gtrsim 940$ Myr). A correct interpretation of observational data requires an in-depth understanding of the transport and mixing dynamics of chemical elements in the Universe. Theoretical models predict their extremely nonuniform distribution in a range from the interstellar medium on spatial scales of a few hundred light years to the intergalactic medium spanning tens of millions of light years. This is observed in absorption spectra of quasars up to redshift $z\sim 6$ and results in observational selection. The review focuses on the early stages of the history of the Universe's chemical enrichment as it is currently understood given the observational selection effects. Observational data and theoretical ideas underlying the modern understanding of the complex process of the Universe's chemical evolution are outlined.
Uspehi fizičeskih nauk. 2023;193(11):1137-1161
1137-1161
Physics of our days
Quantum entanglement, teleportation, and randomness: Nobel Prize in Physics 2022
Abstract
Precise control for individual quantum systems, such as individual photons, atoms, or ions, opens the door to a range of quantum technologies. The goal of this concept is to create devices that, due to quantum effects, will be able to solve prob„lems of data processing and secure information transfer and high-precision measurements of parameters of the surrounding world more effectively than existing approaches do. The key step in the advent of quantum technologies was the pioneering work of the second half of the twentieth century, which, first, showed the paradoxical nature and correctness of the quantum mechanical description of nature and, second, laid down and introduced the basic experimental approaches that became the basis of modern quantum technologies. The Nobel Prize in Physics 2022 was awarded to Alain Aspect, John Clauser, and Anton Zeilinger for their experiments with entangled photons, establishing the violation of Bell inequalities, and pioneering quantum information science.
Uspehi fizičeskih nauk. 2023;193(11):1162-1172
1162-1172
Instruments and methods of investigation
Laser reduction of graphene oxide: local control of material properties
Abstract
We present a detailed analysis of the available data on the laser reduction of graphene oxide (GO). Issues of GO synthesis, structural models, and methods for controlling the properties of the material are considered. The chemical and thermal reduction mechanisms, the two main photoinduced mech„anisms for the transformation of dielectric GO films into conducting structures, are described, and their combined effect is illustrated. The impact of laser radiation parameters on the local functionalization of the material, which determines its properties, is critically analyzed. A summary table of the available data on the laser effect on GO is presented. Various applications are outlined, such as electronics, photovoltaics, energy, and flexible sensors, including medical applications. This study systematizes the results presented in the literature and contributes to the further study of the interaction of laser radiation with carbon materials, their transformation, control of properties, and the potential for application in all-carbon electronics.
Uspehi fizičeskih nauk. 2023;193(11):1173-1204
1173-1204
Methodological notes
Unitarity relation and unitarity bounds for scalars with different sound speeds
Abstract
We consider a theory which contains massless scalar fields with different sound speeds. For these theories we derive unitarity relations for partial wave amplitudes of $ 2 \to 2$ scattering, with explicit formulas for contributions of two-particle intermediate states. We also obtain unitarity bounds both in the most general case and in the case considered in the literature for the speed of sound, equal to unity. We illustrate our unitarity relations by explicit one-loop calculation to the first nontrivial order in couplings in a simple model of two scalar fields with different sound speeds. Obtained unitarity bounds can be used to estimating the strong coupling scale of a pertinent effective field theory (EFT).
Uspehi fizičeskih nauk. 2023;193(11):1205-1213
1205-1213
Laminar submerged jets of incompressible fluid at large Reynolds numbers
Abstract
Fundamental theoretical studies on laminar axisymmetric submerged jets are considered. The problems associated with jets with a flow rate through the initial cross section and with swirling jets are investigated. Some erroneous results of the theory of laminar jets have been discovered and corrected.
Uspehi fizičeskih nauk. 2023;193(11):1214-1226
1214-1226
‘Quantum’ values of the extrema of ‘classical’ macroscopic quantities
Abstract
Fundamental constants play an important role in nature. They determine many high-energy processes. It turns out that these constants also set bounds for the ‘ordinary’ properties of condensed matter, such as viscosity, thermal conductivity, elastic moduli, and the speed of sound. Kinematic viscosity has a global minimum point on the $(P, T)$ diagram, and the same is true for the thermal diffusivity of substances (except at the critical point). The minimum values of these quantities are determined only by the Planck constant $\hbar $ and the masses of the electron $m$ and the atom or molecule $ M$. A nontrivial conclusion is that the kinematic viscosity values for ordinary fluids and for quark–gluon plasma are close to each other. Similarly, the extrema of the elastic characteristics of substances, the mechanical properties of materials, and the speed of sound are also determined only by the Planck constant, the masses of the electron and ions, and the electron charge. The use of fundamental constants allows proposing reasonable estimates for the speed of sound of substances and the elastic characteristics of low-dimensional systems. We also note a possible connection between extreme values of macroscopic quantities and the anthropic principle.
Uspehi fizičeskih nauk. 2023;193(11):1227-1236
1227-1236
Machine learning for the search for topological spin textures
Abstract
We present an alternative method for numerical modeling of topological magnetic textures using a neural network algorithm. We discuss a model of localized spins where topological magnetic textures are stabilized due to a delicate interplay between the symmetric exchange interaction, and the antisymmetric interaction caused by exchange–relativistic effects, as well as a model of an itinerant magnet where noncoplanar spin configurations emerge when taking multispin interactions into account. The viability of the proposed method is illustrated with the formation of lattices of skyrmions and antiskyrmions, magnetic hedgehogs, and skyrmion tubes in two-dimensional and three-dimensional magnetic systems.
Uspehi fizičeskih nauk. 2023;193(11):1237-1247
1237-1247
Physics news on the Internet: November 2023
Uspehi fizičeskih nauk. 2023;193(11):1248-1248
1248-1248