The concept of entropy is not uniquely relevant to the statistical mechanics but, among others, it can play pivotal role in the analysis of a time series, particularly the stock market data. In this area, sudden events are especially interesting as they describe abrupt data changes with potentially long-lasting effects. Here, we investigate the impact of such events on the entropy of financial time series. As a case study, we assume data of the Polish stock market, in the context of its main cumulative index, and discuss it for the finite time periods before and after outbreak of the 2022 Russian invasion of Ukraine. This analysis allows us to validate the entropy-based methodology in assessing changes in the market volatility, as driven by the extreme external factors. We show that some qualitative features of such market variations can be well captured in terms of the entropy. In particular, the discussed measure appears to highlight differences between data of the two considered timeframes in agreement with the character of their empirical distributions, which is not always the case in terms of the conventional standard deviation. Moreover, the entropy of cumulative index averages, qualitatively, the entropies of composing assets, suggesting capability for describing interdependencies between them. The entropy is also found to exhibit signatures of the upcoming extreme events. To this end, the role of recent war in shaping the current economic situation is briefly discussed.

Recent studies confirmed that the long-searched-for phonon-mediated superconducting phase in graphene may be induced via lithium deposition. However, it is also suggested that lithium-decorated graphene (${\mathrm{LiC}}_6$) behaves as a canonical superconductor, despite the moderate electron-phonon coupling constant and low Fermi energy in this material. Herein, this issue is addressed within the isotropic Eliashberg formalism in the adiabatic and nonadiabatic regimes to account for the potentially pivotal effects hitherto not captured. The conducted analysis indicates signatures of the nonadiabatic superconductivity in ${\mathrm{LiC}}_6$ and the resulting effects on the selected thermodynamic properties. It is shown that although the critical temperature obtained in the nonadiabatic regime is similar to the earlier estimates ($\sim 6$ K), its value corresponds to the smaller magnitude of the Coulomb pseudopotential than previously expected. Moreover, the characteristic ratio of the pairing gap and the inverse temperature is found to notably exceed estimates of the BCS theory. In what follows, the obtained results attempt to present coherent interpretation of the superconducting phase in ${\mathrm{LiC}}_6$ and vital insight into its fundamental properties. Moreover, they allow us to draw potential directions for future research on low-dimensional superconductivity by reveling that many other graphene-related superconductors may be subject to nonadiabatic effects. This aspect appears to be essential for the design of new two-dimensional hexagonal superconductors aimed at relatively high critical temperature values.

Unknown quantum electronic conductance across nanojunctions made of silicon-doped carbon wires between carbon leads is investigated. This is done by an appropriate generalization of the phase field matching theory for the multi-scattering processes of electronic excitations at the nanojunction and the use of the tight-binding method. Our calculations of the electronic band structures for carbon, silicon, and diatomic silicon carbide are matched with the available corresponding density functional theory results to optimize the required tight-binding parameters. Silicon and carbon atoms are treated on the same footing by characterizing each with their corresponding orbitals. Several types of nanojunctions are analyzed to sample their behavior under different atomic configurations. We calculate for each nanojunction the individual contributions to the quantum conductance for the propagatingσ,Π, andσ^∗electron incidents from the carbon leads. The calculated results show a number of remarkable features, which include the influence of the ordered periodic configurations of silicon-carbon pairs and the suppression of quantum conductance due to minimum substitutional disorder and artificially organized symmetry on these nanojunctions. Our results also demonstrate that the phase field matching theory is an efficient tool to treat the quantum conductance of complex molecular nanojunctions.

Motivated by the growing interest in the nonmetricity-matter couplings, we develop the scalar–tensor formulation of recently introduced f(Q, T) gravity, where Q is the nonmetricity and T is the trace of the energy–momentum tensor. The main properties of the scalar–tensor formalism for the Friedmann–Lemaître–Robertson–Walker (FLRW) Universe are discussed, and we introduce an appropriate set of dynamical variables to analyze the cosmic evolution of the scalar–tensor f(Q, T) cosmology as a dynamical system. By considering two distinct cosmic fluids, namely matter and radiation, we have demonstrated that the cosmological phase space exhibits the typical curvature-dominated, radiation-dominated, matter-dominated, and exponentially accelerated fixed points. Furthermore, under an appropriate set of initial conditions compatible with the current observations from the Planck satellite, our analysis shows that the scalar–tensor f(Q, T) successfully yields models indistinguishable from the $$\Lambda $$ Λ CDM cosmology and compatible with the weak-field solar system dynamics, without the inclusion of a cosmological constant $$\Lambda $$ Λ . Thus, the theory introduced herein may be regarded as a suitable candidate to describe the cosmological dynamics of the Universe.