Physics of Wave Phenomena最新文献

An apodized Fiber Bragg Grating (FBG) is designed to obtain minimal quantity of side lobes on the reflection spectrum for effective estimation of temperature sensitivity. Bare FBG cannot be implemented as a suitable option for sensing of temperature in a complex environment because it is composed of silica, which has a very low thermal expansion coefficient. Different kinds of materials having thermal expansion coefficients higher than silica are coated on designed apodized FBG to improve the sensitivity of temperature for the FBG. In this simulation work, titanium, nickel, gold, copper, silver, aluminum, lead, indium, polycarbonate, PMMA, and polyamide are coated on the apodized FBG to estimate the enhanced sensitivity for the temperature range of 25 to 75°C. The simulation results illustrated that the sensitivity of temperature for polyamide-coated FBG is highest than other coating materials.

Due to the extremely superior ability of ultrathin metasurfaces to reconstruct the wavefront, the study of the invisibility cloak is possible. However, the currently designed stealth cloak still has narrow bandwidth and application angle limitations, affecting the performance of the stealth cloak. In this paper, a highly variable transmission phase unit structure is proposed, and a dielectric metasurface carpet stealth cloak is constructed to achieve broadband and wide-angle characteristics. The proposed metasurface can effectively suppress scattering and reconstruct the wavefront. The carpet stealth cloak can realize the reflected wavefront control characteristics in the microwave range of 5 to 8 GHz, and can achieve stealth characteristics at the angle of incidence of 80°.

In the present article, we analyzed the effects of Tsallis (or nonextensive) polarization force on nonlinear dust acoustic waves (DAWs). The polarization force acting on dust particles in a nonuniform dusty plasma is then revisited within the theoretical framework of the nonextensive statistical mechanics. The behavior of the polarization force is considerably changed due to the presence of nonextensive ions. Specifically, we showed that, for both experimental and space dusty plasmas, the magnitude of the polarization force (in the case where q > 1) increases as the ion nonextensivity becomes significant. As an application, we studied the changes caused by the nonextensive polarization force on the intrinsic properties of the DAW, namely, the wave profile, the transported energy, and the electric field. In particular, we have shown that due to the presence of nonextensive polarization force, the DA wave profile becomes deeper and the transported energy undergoes depletion. For a good understanding, we have also carried out a comparative study on the effects of the nonextensive polarization force on the DAW and its energy associated with both space and experimental dusty plasmas. We have found that, for a given value of the nonextensive parameter q, the DAW profile of the experimental dusty plasma seems more affected by the presence of the Tsallis polarization force.

A two-dimensional system characterized by the Hertz potential with the parameter α = 7/2 in the region of crystal-phase stability has been studied by the molecular dynamics method. It is shown that the anomaly of the density and thermal expansion, found previously for this system in the equation of state along isochores, also manifests itself on isotherms. A study of the translational and orientational order parameters revealed their drop in the density anomaly region, which is most pronounced for the translational order parameter. The obtained results are also in good agreement with the previous data on the attenuation of the transverse phonon mode in this region. This correlation indicates the presence of a strongly diffuse isostructural transformation in the anomalous region of the phase diagram.

The results are reported of processing luminescence spectra from samples obtained by successive dilution of the aqueous solution of antibodies to S100 protein with the initial concentration C = 1 µM. It is found that the intensity of the light scattering background increases as compared to the control water, which indicates relaxation of optical properties of the solution, probably due to modification of its structure at successive dilution.

The structure of aqueous solutions has been studied for a long time; however, many things still remain unclear. One of the ways to describe the water structure is the statistical approach, within which the distribution of water molecules over mobility, connectivity, number of hydrogen bonds, etc. is analyzed. An important parameter in this consideration is the equilibrium number of free water molecules, which are not bound by hydrogen bonds and do not enter the composition of hydrate shells. There are not any completely justified approaches for calculating the fraction of free water molecules in solutions. Aqueous solutions are known to have a weak band of the relaxation type (differing from the classical Debye relaxation band) in the THz frequency range. This band is assigned to the orientational relaxation of free water molecules. In this paper we theoretically consider the process of orientational relaxation of free water molecules in an aqueous solution in the THz range. The theory is based on the Onsager polarization model, modified for application in the THz range. The field screening due to the higher frequency polarization processes is taken into account. Particular attention is paid to the field screening due to the orientational polarization of bound water molecules. Based on this consideration the ratio between the fractions of free water molecules in solution and the parameters of spectral bands of water molecular dynamics is obtained. The calculated numbers of free water molecules, obtained within the proposed theory and other known (simpler) approaches, are compared for some solutions. It is shown that, if the field screening is taken into account when considering the orientational polarization of free water molecules, their number increases. For example, the number of free molecules for liquid water at 25°С, with complete consideration of screening, is about 9%.

A comparative study of the sizes and spatial structure of single dielectric colloidal nanoparticles of lanthanum fluoride, doped with rare-earth neodymium ions (Nd³⁺:LaF₃), and their conglomerates in an aqueous solution has been performed. Nanoparticles were synthesized by aqueous co-precipitation method with subsequent hydrothermal microwave (HTMW) treatment. Experiments were performed using three methods: transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and dynamic light scattering (DLS). An analysis of the results has shown that a stable colloidal solution of nanoparticles is formed during synthesis. The solution consists of single lanthanum fluoride nanoparticles, having a narrow (10–30 nm) size distribution, and nanoclusters formed on their basis. It is also shown that the spatial structure of nanoclusters cannot be described in terms of the fractal model, which is widely used to describe clusters formed in colloidal solutions of nanoparticles of various nature.

A procedure is discussed for obtaining various solutions to the Schrödinger equation by the Monte Carlo method. Water clusters, namely, the hexamer 6(H₂O), dodecamer 12(H₂O), and tetradecamer 14(H₂O) are used as quantum systems to illustrate the procedure. Various solutions to the Schrödinger equation are derived from the algorithm earlier proposed by the author, which is based on the intersection of the finite-difference and Monte Carlo approaches and on the water-cluster-tested methods for spatially reducing scattering centers of particle nuclei and scattering centers of electrons of an arbitrary quantum system. Ultimately, it has become possible to construct an algorithm for generating an unlimited number of various spatial structures of scattering clouds of particle nuclei and electrons at a given dissociation energy of a quantum system.

Analysis of the results of nonempirical simulations of Met⁺(H₂O)_n clusters with Met = Li, Na, and K, and n = 20–55 carried out at the density functional level with B3LYP exchange-correlation functional and extended double-zeta basis sets revealed the prevailing structure motifs of the aqua complexes of alkali metal ions and their fingerprints in the infrared absorption spectra in the range of 2000–4000 cm^–1. The hydration structures of the ions are found to be predetermined by the balance between the conjugated H-bonded rings and extended ordered H-bonded sequences. The extension of the latter is shown to decrease with an increase in the effective radius of the ion, which is reflected in the stronger localization of the coupling of OH oscillators within the homodromic structural rings and the respective shift in the characteristic frequencies within the OH stretching domain.