The entire world has been suffering from the coronavirus disease 2019 (COVID‐19) pandemic since March 11, 2020. More than a year later, the COVID‐19 vaccination brought hope to control this viral pandemic. Here, we review the unknowns of the COVID‐19 vaccination, such as its longevity, asymptomatic spread, long‐term side effects, and its efficacy on immunocompromised patients. In addition, we discuss challenges associated with the COVID‐19 vaccination, such as the global access and distribution of vaccine doses, adherence to hygiene guidelines after vaccination, the emergence of novel severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) variants, and vaccine resistance. Despite all these challenges and the fact that the end of the COVID‐19 pandemic is still unclear, vaccines have brought great hope for the world, with several reports indicating a significant decline in the risk of COVID19‐related infection and hospitalizations.
Introduction:The relative simplicity of one-dimensional models often helps to solve the problem in an analytical form from the beginning to the end. For many years, one-dimensional models have retained attractive for a qualitative description of quasi-particle spectra and consequently physical characteristics of solids (see, e.g., [1]. Nondegeneracy of the energy eigenvalues and the absence of singularities on the spectral densities within the continuous spectrum band significantly simplify the problem of determining spectra perturbations induced by various defects [1,2]. At once it should be noted that the formation of localized states in lowdimensional and three-dimensional systems are quite different (see, e. g., [3]). On the one hand, the use of one-dimensional models for the description of vibrations localized on defects in threedimensional crystals reduces the value of this description. On the other hand, the zero-threshold forming of local discrete levels outside the quasi-continuous spectrum band and the strong dependence of energy levels on the defect parameters are of great general importance including applied purposes.The in-stability of the crystalline phase of one-dimensional structures is the main disadvantage for the description of phonon spectra and vibrational characteristics of real systems.There is no long-range order in one-dimensional systems because even at its mean-square displacements diverge [4]. However, if the phonon spectrum of a linear chain starts with a frequency different from zero, this divergence disappears and thus the linear chains can exist in reality and can be studied experimentally. They can exist as the linear chains of atoms in the bulk or on the surface of some solid matrices, i.e., quasi-chains of carbon atoms between graphene monolayers on silicon substrates [5] and chains of gold atoms deposited on the silicon surface [6-8]. The bundles of closed at the ends nanotubes enriched with gases containing quasi-one-0 T =
Phonon and electron spectra of metallic bigraphene are analyzed in the presence of step-edge crystal imperfection. Different geometries of step-edge are considered. The dynamic planar stability of the considered structure is proved for temperatures above the ambient. The number of phonon states is shown to grow near the K-point of the first Brillouin zone, compared to pristine graphene. It is found, that this type of defects causes substantially nonuniform distribution of electron states and the pronounced increase in the number of states with energies close to Fermi energy can be expected in electron spectrum of the graphene-based compounds. The performed calculations are in good agreement with inelastic neutron, x-ray and Raman measurements.
Calculations on a microscopic level are used to explain the experimentally observed negative linear thermal expansion along some directions in a number of crystalline compounds with complicated lattices and anisotropic interactions between atoms. Anomalies in the temperature dependence of the coefficient of linear thermal expansion are analyzed in layered crystals made up of monatomic layers (graphite and graphene nanofilms) and multilayer “sandwiches” (transition metal dichalcogenides), in multilayered crystal structures such as high-temperature superconductors where the anisotropy of the interatomic interactions is not conserved in the long-range order, and in graphene nanotubes. The theoretical calculations are compared with data from x-ray, neutron diffraction, and dilatometric measurements.
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