Physics of Wave Phenomena最新文献

The LiGaSe₂ and LiGaS₂ crystals with antireflection microstructures are comparatively tested as frequency down-converters into the mid-infrared range (4874 nm) in a two-stage optical parametric oscillator with a single cavity under intracavity pumping with a Nd:YLF laser with a wavelength of 1047 nm and a pulse duration of 25 ns. The first stage of optical parametric oscillation in the KTiOAsO₄ crystal produces two-micron radiation with wavelengths of 1724 and 2668 nm at a pulse energy of up to 2 mJ. In the second stage of conversion, the LiGaS₂ crystal with antireflection microstructures compared to LiGaSe₂ with antireflection microstructures proves to be more efficient despite the lower effective nonlinearity coefficient, which can be explained by the higher optical quality of the crystal. The energy of the radiation pulse with a wavelength of 4874 nm reaches the level of 100 nJ.

It is shown that the structures of ices III and V can be divided into nearly identical chiral layers. In achiral ice V, the right-handed enantiomorphic layers alternate with the left-handed ones. Chiral ice III consists of only right-handed or only left-handed layers. A structural mechanism preserving these layers is proposed for the transitions between ices III and V. This mechanism is partially diffusive. The possibility for the proposed structural mechanism to provide the experimentally observed high transition rate is discussed. Small structural units of crystal ices are shown to change regularly with increasing pressure in the sequence III, V, and VI. Such small structures formed by water molecules can be present in liquid near the crystallization curve.

Two fundamental questions of modern theoretical physics—the paradox of radiant power and the issue of localized currents—are discussed in the paper. The radiant power paradox is the dilemma of whether electrodynamic systems radiate power outward or not. Mathematical analysis of the microscopic Maxwell equations describing excitation and propagation of electromagnetic fields shows that the total radiant power should be zero, whereas many classical problems considering localized currents argue the opposite. The paradox is resolved by proving limited applicability of localized-current models to calculations of energy and momentum characteristics of electromagnetic fields. The nonzero value of the total radiant power for these currents turns out to be the localized current approximation error, while the true radiant power value is always zero for physically consistent excitation currents. On the basis of analysis of physically consistent currents, an improved model of localized currents is proposed that enables physically consistent description of electromagnetic fields from the viewpoint of their energy and momentum characteristics but at the expense of causality violation in the external current-free region.

Self-assembly of colloidal particles may occur, for example, both under the action of external fields and due to the presence of pinning centers in a real experimental system. Of particular interest is the formation of condensed phases from an aqueous solution of colloidal particles on a substrate in an external rotating magnetic field. Substrate defects (for example, the substrate roughness) are of great importance in an experiment. These defects can act as pinning centers, to which colloidal particles are strongly attracted; this may lead to a change in the melting scenario. Changing the field rotation angle, one can obtain different colloidal structures. At small rotation angles, the system behaves like a two-dimensional system with a purely repulsive soft-disk potential, whereas at large angles it is similar to a generalized Lennard-Jones (LJ) system with an (nm)-potential. When the field rotates in the plane of the system, its phase diagram qualitatively resembles that of a classical model system with a LJ pair potential. The results of the computer simulation of a two-dimensional system with a LJ potential in the presence of Gauss pinning are discussed in the context of its influence on the phase diagram and melting scenario. It is shown that random pinning with a Gauss potential leads to an increase in the hexatic phase range; formation of dense clusters near pinning centers, which reduce the average effective density of the system; and a change in the melting scenario.

The fiber-optic Fabry–Perot interferometer (FPI) has been analyzed to determine its reflection and transmission coefficients providing the maximum useful signal in a high-precision scheme for measuring the FPI length. It is shown that the traditionally applied criterion, which is aimed at achieving the maximum visibility of the interference pattern, is not applicable in this scheme. An adequate criterion is proposed, and an analysis based on it is presented. The optimal characteristics of the FPI mirrors are calculated taking into account the diffraction effects. The result of the study is a set of simple analytical relations necessary for designing mirrors in the form of thin films deposited on the fiber end face. In particular, the possibility of implementing a desired mirror on the fiber end in the form of a single-layer dielectric film is investigated and its characteristics are obtained.

Gold nanoparticles are widely used in spectroscopy for detecting/studying substances in biological media. Such particles in biological objects inevitably interact with proteins, which obviously affects the functions and properties of the nanomaterial. The influence of external conditions on the interaction of nanoparticles with proteins in the aqueous phase has still remained little studied. In this paper we investigate the influence of temperature and pH of the medium on the interaction of lysozyme protein with gold nanoparticles in aqueous solutions. It is found that the temperature of the medium affects the size of aggregates of gold nanoparticles with protein at pH 7.5 of the aqueous solutions. It is found that lysozyme prevents protein aggregation at acidic pH values; with an increase in temperature, gold particles with a lysozyme protein crown retain their size. The results of this study gain a deeper insight into the processes of interaction between enzymes and gold nanoparticles with a change in the solvent properties.

The results from field measurements of hydrological characteristics of the Kara Sea water during the expedition on the research vessel Professor Molchanov in the summer of 2024 are reported. Vertical oscillations of temperature at fixed depths (vertical liquid oscillations) caused by short-period background internal waves are detected in the thermocline using extended “yo-yo” CTD profiling synchronous with an independently operating buoy-mounted thermistor chain. Their considerable effect on the vertical temperature distribution is shown. Energy spectra of the above-mentioned oscillations are obtained. It is demonstrated that the region under consideration near Novaya Zemlya can be regarded as a region where background internal waves quite often occur. The statistical characteristics of the fields of these waves are compared to those of similar wave fields on the Atlantic shelf and near the Kamchatka shore.

A series of Tm,Li:ZnWO₄ single crystals with different combinations of thulium and lithium concentrations is grown by the Czochralski method. Actual concentrations of both dopants are measured using inductively coupled plasma mass spectrometry. Segregation coefficients of thulium and lithium in the crystals are calculated by the initial point method. It is shown that introduction of lithium into the crystal composition increases the segregation coefficient of thulium between the crystal and the melt by at least a factor of 2, from 0.2 to 0.4. At the same time, the segregation coefficient of lithium monotonically decreases from 0.18 to 0.08 with its increasing concentration. Thus, to produce a sample with considerable and equimolar Tm and Li concentrations in the crystal, the nominal concentration of lithium is required to be very high, severalfold higher than that of thulium. Polarized optical absorption spectra of the crystals are measured at room temperature for all possible combinations of orientations of the strength vectors of the test beam’s electric and magnetic fields with respect to the optical indicatrix axes of the crystals. It is shown that at the electric field orientation E || N_m the shape of the absorption spectra appreciably depends on the magnetic field orientation as well. The influence of the lithium presence/absence in the crystal on the shape of the absorption spectra is determined. Absorption cross sections of thulium in the given crystal are refined and found to be considerably larger than previously published. Mechanical strength characteristics, microhardness and fracture toughness, are measured for the series of Tm,Li:ZnWO₄ crystals using the indentation method. It is shown that these characteristics are noticeably deteriorated when Tm³⁺ ions are introduced into the crystal without simultaneously introducing the charge compensator—Li⁺ ions—because there arise zinc vacancies that loosen the crystal structure. Additional introduction of lithium in equimolar amounts results in that the strength characteristics of the crystals are not only restored but even exceed those of undoped ZnWO₄, since this simultaneous doping does not lead to formation of zinc vacancies. Thus, conditions are revealed that allow fabrication of heavily thulium-doped crystals with maximum possible mechanical strength characteristics of ZnWO₄.

The spin selectivity of the processes occurring in vapor above the surface of boiling water has been experimentally demonstrated. This selectivity leads to a significant increase in the fraction of ortho-H₂O molecules in vapor. An increase in the relative content of ortho/para-isomers of water from the equilibrium value of 3 : 1 (determined by quantum statistics) to 5 : 1 was observed. The content of H₂O spin isomers in vapor above the water surface was analyzed using a tunable diode laser. Spectral analysis of the ortho- and para-H₂O content was performed using the absorption lines of these molecules belonging to the vibrational–rotational band 101-000 and having transition frequencies of 7355.557 and 7354.599 cm^–1, respectively. When water is heated from room temperature (20°C) to the second boiling phase (~80°C), a ratio of ortho- and para-spin isomers of ~3 : 1 was observed, which is typical of normal conditions. During the second and third boiling phases (80–90°C), the ortho/para ratio increases to 5:1. A possible mechanism for increasing the fraction of ortho-H₂O in the vapor formed during boiling may be associated with the depletion of the equilibrium mixture in the para-H₂O isomer, due to its higher activity in condensation and formation of water microdrops, dimers, and trimers.

Numerical simulation is used to compare two methods for measuring power of wideband electromagnetic noise in experimental facilities with high-current relativistic electron beams formed by explosive-emission cathodes. The simulation shows that the difference in the experimental results by two orders of magnitude—several megawatts for pulses with a duration of few nanoseconds and tens of kilowatts for pulses with a duration of hundreds of nanoseconds—arises from the nature of the noise itself at different stages of the explosive-emission cathode operation rather than from difference of the measurement methods.