Physics of Wave Phenomena最新文献

Probable structural mechanisms with structural invariants based on a chain of six-membered cycles linked through a common atom are proposed for some transitions between crystal water phases. It is shown that in the II → Ic transition with the structural invariant under consideration, 5/6 of the hydrogen bonds of the initial structure are retained, while in the same transition considered previously with the structural invariant in the form of a band of six-membered cycles linked through a shared bond, only 3/4 of the bonds of the initial structure are retained. In the V → Ic transition, both structural invariants (chains of six-membered cycles linked through a common atom and bands of six-membered cycles linked through a shared bond) are shown to be retained simultaneously. For the structural mechanism of the V → Ic transition with these structural invariants, 11/14 of hydrogen bonds of the initial structure are retained. It is shown that structural invariants of the mechanisms for the IX → Ic, VI → Ic, IX → II, and II → III transitions may also be based on a chain of six-membered cycles linked through a common atom.

The thermodynamic properties of hafnium under the high pressures obtained behind the shock wave front are described. A simple model in the form of a dependence of pressure on the specific volume and specific internal energy is proposed. The thermodynamic characteristics of the body-centered cubic (bcc) solid phase and melt of hafnium under high shock-compression pressures are calculated. The calculation results are compared with the available data of shock-wave experiments. The resulting equation of state of hafnium can be used in numerical simulation of the processes occurring at high pressures in shock waves.

The role of hydrogen peroxide molecule (Н₂О₂) in the vital functions of biological objects has been considered. The mechanisms of Н₂О₂ formation and its relationship with redox reactions, as well as some possible methods of analyzing the Н₂О₂ content in liquid and gaseous media, are discussed. In particular, the possibility of using highly sensitive methods of laser spectral analysis for detecting Н₂О₂ traces in exhaled air, which are promising for diagnostics of various pathologies, is considered. The absorption spectra of exhaled air are analyzed, and the strongest H₂O₂ spectral lines (isolated from the influence of other gaseous metabolites), applicable for detecting Н₂О₂ by diode laser spectroscopy, are chosen.

The application of wide-gap semiconductor nanoparticles for improving optical characteristics of dye-sensitized solar cells (DSSCs) is considered. Here, silicon carbide nanoparticles (nSiC) are used as wide-gap quantum dots, and chromophores (lutetium diphthalocyanine and delphinidin) play the role of sensitizers. The influence of SiC nanoparticles on the absorption spectra of chromophores in tetrahydrofuran solutions, as well as their direct influence on substrates with titanium dioxide after introduction of sensitizers, is investigated. The characteristics of designed DSSCs are measured, and the DSSC performance is estimated based on the measurement data. The DSSC power and efficiency are calculated. It is found that addition of wide-gap semiconductor nanoparticles to a sensitizer improves significantly the characteristics of solar cells and increases essentially their stability. This improvement can be explained by the exciton decay, at which an electron passes initially to a nanoparticle of wide-gap SiC and then to a titanium dioxide (TiO₂) nanoparticle. The best characteristics of the solar cell versions under consideration correspond to those obtained for delphinidin with SiC nanoparticles.

Adiabatic compressibility β_S of the 4-methylpyridine + water solution is investigated in a wide concentration and temperature variation interval using Mandelstam–Brillouin scattering spectroscopy. The adiabatic compressibility minimum caused by the microinhomogeneous structure of the solution is experimentally established at the concentration of 0.06 M. The results of the investigations allow constructing a diagram of possible states caused by a continuous three-dimensional hydrogen bond network of water.

A technique of two-stage three-dimensional mapping of the optical breakdown threshold in diamond crystals is proposed. In the first stage diamond is irradiated by high-energy ultrashort laser pulses, which initiate multiple microbreakdowns in the probed volume of material; these breakdowns cause formation of graphite microinclusions. A sharp decrease in the spatial density of microinclusions in some crystal zone indicates a significant increase in the average value of breakdown threshold in this zone as compared with the neighborhood. The second stage of mapping implies measurement of the absolute values of breakdown threshold by choosing the minimum laser pulse energy necessary for the formation of a graphite microinclusion at a point studied. The “abnormal” crystal zones revealed in the first stage are investigated especially thoroughly, with optimal spatial resolution. Application of this technique to synthetic diamond single crystals from different manufacturers, grown by chemical vapor deposition (CVD), revealed zones in these crystals where the breakdown threshold changes by a factor of more than 10. The boundaries of these zones are located parallel to the (100) growth face; the layer thickness and position vary unpredictably.

Investigation is carried out to experimentally study concentration of microwave radiation with a wavelength ranging from 2.46 to 3.55 cm in a compact subwavelength region by a spherical resonator consisting of a dielectric sphere with a waveguide branch 1.15, 2, or 2.26 mm in diameter connected to the sphere tangentially to its surface or normally along its radius. The microwave radiation with a frequency ranging from 8.45 to 12.2 GHz excites Mie resonance oscillations in the spherical resonator with the attached waveguide branch. Frequency dependences of radiation from the waveguide branches show that the radiation intensity at the Mie resonance is almost two orders of magnitude higher than the intensity of the radiation exciting the resonant sphere.

Structural transformations under chlorine adsorption on the Ag(100) surface have been studied with scanning tunneling microscopy (STM) and within the density functional theory (DFT) calculations. The DFT method reveals that the preferable adsorption site of chlorine atoms is the fourfold hollow position. The STM technique is used to study the disorder–order structural phase transition occurring at a gradual increase in the chlorine coverage, which results in formation of the с(2 × 2) structure on the Ag(100) surface. It is found that the critical coverage of the ordering corresponds to ≈0.34–0.35 monolayer (ML). The chemisorbed chlorine monolayer is saturated at the coverage of 0.5 ML corresponding to the formation of the c(2 × 2) structure. Further chlorine absorption leads to nucleation and growth of AgCl islands near the edges of atomic steps.

Further evidences of effectiveness of а two-dimensional approach to modeling of three-dimensional deep-water potential waves are given. The 2-D model is based on the same two surface conditions as 3-D, but instead of а 3-D Laplace equation (used routinely for calculation of surface vertical velocity) the surface projection of Laplace equation is suggested for use. This equation is not closed, since it contains both the vertical velocity and its vertical derivative. The closing scheme is based on consideration of vertical structure of a nonlinear component of the velocity potential. It was shown before that the surface vertical velocity and its derivative are linearly connected with a coefficient depending on some integral parameters of the problem. The applicability of the 2-D model for reproducing statistical properties of wave field was demonstrated before for relatively simple integral characteristics and spectra. The paper is devoted to comparison of more complicated statistical results generated by full 3-D model and current 2-D model. A good agreement between the high order moments for elevation and surface vertical velocity and some other characteristics proves the applicability of the model for reproducing of statistical structure of a multimode wave field with satisfactory accuracy. The main advantage of 2-D model is that it runs 30–80 times faster than a 3-D model with similar setting.

The electronic properties of magnetic semiconductors TlFeS₂ and TlFeSе₂ have been investigated experimentally by spectral ellipsometry and theoretically ab initio using the density functional theory (DFT). The imaginary and real parts of the dielectric function and the dispersion of the refractive indices, extinction coefficients, and absorption coefficients are found from ellipsometric measurements in the energy range of 0.7−6.5 eV. The direct band gap is estimated. The band structure, the origin of energy states, the optical functions, and the partial densities of states (PDOS) projected on atoms are determined from ab initio calculations. The calculation results are compared with the spectral ellipsometry data obtained in this study.