Physics of Wave Phenomena最新文献

An original waveguide design for the GaAs/AlGaAs quantum cascade laser with the wavelength of 10 µm and the substrate-leaking mode is proposed. Electromagnetic fields in the proposed waveguide are simulated, and the radiation pattern is calculated in the plane perpendicular to the structure growth plane. Feasibility of this laser with the radiation divergence of less than 4° is shown.

The frequency dependence of sound velocity in the frequency range from 5.4 MHz to 6.1 GHz in an aqueous solution of 4-methylpyridine with a concentration corresponding to the singular point has been experimentally studied. The specific features of the positive sound dispersion and the found negative dispersion in a narrow range of hypersonic frequencies are discussed from the viewpoint of different structural organization of the solution components in the temperature ranges below and above the singular point temperature. An experimental indication of the existence of a structural phase transition in the solution at a temperature below the singular point, described within the mean-field approximation of Landau theory, has been obtained.

Tunable diode laser absorption spectroscopy methods are applied to study gas biomarkers of gut microbiota activity. For this purpose, a hardware and software complex (HSC DLS) and a technique for multicomponent measurements of gas biomarkers in exhaled air are developed. The complex consists of a high-resolution multichannel tunable diode laser spectrometer based on four single-mode near-IR diode lasers with a fiber optic output for measuring O₂, ¹²CO₂, ¹³CO₂, CH₄, NH₃, H₂S, and H₂O gas contents, a Herriott multipass cell with a total optical length of 35 m, and a semiconductor selective sensor for background measurements of hydrogen concentrations. To find the concentration, the cross-correlation technique for processing spectra using generalized linear/nonlinear regression is employed. Concentrations of exhaled and gut gases have been measured both in experiments on laboratory animals and in clinical studies on 25 patients. For this purpose, hydrogen–methane and lactulose loading tests have been used. Highly accurate measurements of exhaled and gut gas concentrations performed on the HSC DLS allow continuous online measurement of the composition of gut microbiota biomarkers, assessment of the enzymatic activity and taxonomic composition of the microbiota, and non-invasive diagnosis of various gastro-intestinal diseases.

The maximum detection range for an underwater noise source in the presence of internal waves, conditioning the sound-field mode coupling, has been estimated in the framework of holographic processing of hydroacoustic broadband signals. The estimation was performed based on the results of numerical simulation of the sound field decay with distance and experimental data on the spectral characteristics of the noise emission of a moving underwater craft and the background interference of the water area. A single receiver and a linear portable antenna have been considered as receiving modules. The input signal-to-noise ratio at which the maximum detection range is attained is estimated. The probabilities of true detection at specified false alarm probabilities are calculated based on the Neumann–Pearson criterion for the input signal-to-noise ratio corresponding to the maximum detection range. A comparative analysis of the maximum detection range in the presence and in the absence of background internal waves is performed.

Equations are obtained that allow for dissipation during propagation of acoustic wave in narrow tubes of variable cross section. The wave transmission coefficient through the tube of a special design is calculated by two methods. It is shown that when viscosity in tubes of variable cross section is taken into account, the continuity equation should be used as the equation of connection between pressure and vibrational speed.

Frequency dependencies of wave properties of a structure consisting of three layers of flexible metasurfaces are experimentally studied. Transmission and reflections spectra are obtained both for individual metasurface layers with conducting elements and for the two-layer and three-layer structures. In the proposed geometry of the structure with individual layers, it becomes possible to noticeably reduce the intensity of the transmitted and reflected waves in the X range of microwave radiation by introducing violated geometry along the direction of electromagnetic wave propagation in the metamaterial structure due to the asymmetric transmission effect.

The formation of dynamic microcavities (DMs) in the asymmetric collision of a single-cycle π‑pulse and a 2π-pulse of self-induced transparency in a two-level medium is investigated theoretically. The numerical solution of the Maxwell–Bloch equations demonstrates that the interaction of pulses leads to the emergence of two DMs, which are separated in space within the medium. Controlling the shape of the microcavities is possible by altering the number of collisions between pulses. These results pave the way for the development of ultrafast tunable optical devices.

The analysis of the possibility of correlating the momenta and coordinates of a quantum oscillator using the Robertson–Schrödinger generalization formalism and the probabilistic concept of quantum mechanics has been continued. A detailed numerical study of the quantum oscillator excitation modes under a classical impact with variable frequency is performed. An analysis of the harmonic dependence of the quantum oscillator energy showed that the oscillator has frequency intervals of parametric instability, in which the oscillation amplitudes grow exponentially. The mean energy also increases, undergoing small oscillations, which are barely noticeable in resonance, and the correlation coefficient oscillates near zero level. The probabilities of leaving the ground state and passing to the second excited state are calculated for the oscillator. The penetrability of quantum tunnel barriers of moderate depth is estimated. It is shown that the increase in the barrier penetrability upon parametric excitation at the resonant frequency may be two to three orders of magnitude higher than at a detuned frequency. The mechanisms of the radical reactions leading to the formation of reactive oxygen species in an aqueous solution under a classical impact are developed. The use of measurable probabilistic representations for describing the states of quantum particles is substantiated.

Etalon dielectric plates based on organosilicon polymers—λ-meters—have been developed for use in rapid estimates of the generation wavelength of submillimeter range sources. The transmission spectra of λ-meters allow to estimate the frequency of narrow-band radiation with accuracy approximately of 1% in the wavelength range from 3 to 0.4 mm.

The nonlinear behavior of electron acoustic solitary waves in an unmagnetized collisionless plasma with the (r, q) velocity distribution of hot electrons, immobile ions, and a cold-electron fluid is investigated theoretically. The propagation of two solitons is studied by obtaining nonlinear Korteweg–de Vries equations in nonplanar (cylindrical and spherical) geometries using the reductive perturbation approach. Computational simulations are performed to investigate the impact of superthermal effects on these nonlinear waves. The findings demonstrate that superthermal hot electrons and various plasma properties (ratio of cold to hot electrons, spectral index of distribution (r, q)) significantly impact the solitons' propagation characteristics.