Internal wave shoaling in nearly linear stratifications

<div> <div> <div> <p>In the theory of internal waves in the coastal ocean, linear stratification plays an exceptional role. This is because the nonlinearity coefficient in KdV theory vanishes, and in the case of large amplitude waves, the DJL theory linearizes and fails to give solitary wave solutions. We consider small, physically consistent perturbations of a linearly stratified fluid that would result from a localized mixing near a particular depth. We demonstrate that the DJL equation does yield exact internal solitary waves in this case. These waves are long due to the weak nonlinearity, and we explore how this weak nonlinearity manifests during shoaling.</p> </div> </div> </div>

Spatial ultrasonic cleaning process control based on its current state evaluation

Ultrasonic cleaning is one of the most promising types of cleaning in terms of environmental friendliness, cost and efficiency. The condition of the cleaning body must be taken into account for optimal control of the ultrasonic cleaning process. This allows you to irradiate only those areas that really need it. The modelling of the process of ultrasonic cleaning of bodies of different configurations and the analysis of the parameters of ultrasonic responses at different stages of cleaning were performed. This allowed us to identify the parameters by which the assessment of the process should be formed. The main parameter was the change in the time of receipt of the threshold value of the signal, and the auxiliary - the change of the nonlinearity coefficient of the second order. The change in the time of receipt of the threshold value of the signal is an indicator of dirt peeling, and the change in the nonlinearity coefficient demonstrates the approach to the final result of cleaning. These parameters became clear input data for the 3-D fuzzy interval controller. The functions of affiliation were defined and the base of rules was formed. Modelling of the ultrasonic cleaning process using the established method of estimating the course of the process and the use of 3-D fuzzy interval controller showed about 35%energy savings.

TWO-COLOR COMPENSATIVE THERMOMETRY WITH CORRECTED ADJUSTMENT USING NONLINEARITY EQUATION OF EMISSIVITY SPECTRAL DISTRIBUTION

The article is directed on metrological characteristics increase and extension of the optical thermometry field of use, including two-color compensative thermometry with a priori averaged adjustment. The investigations have been performed for the tungsten. This metal studied in thermometry and metal optics has tabulated quantitative estimations of emissivity which are similar to the most widespread in metallurgy iron-carbon alloys. To increase the reliability and extend the field of use of obtained results, approximated and linearized spectral distributions of tungsten, as well as their mirror representations with decreasing and increasing, convex, linear, and concave distributions of emissivity have been researched. The influence of qualitative and quantitative characteristics of the spectral distributions of emissivity on their nonlinearity coefficient has been studied. The equation of nonlinearity has been obtained. This equation connects the nonlinearity coefficient at the middle wave with the emissivity value at one of the boundary waves through the measured one-color radiation temperatures at 3 operating waves. With a priori knew quantitative estimates of the nonlinearity coefficient at the middle wave and measured onecolor radiation temperatures, the obtained equation can be used for the calculation of emissivity values at the boundary waves. For example, in the linear spectral distributions of emissivity, the nonlinearity coefficient is equal to 0. The number of solutions for linear distributions of emissivity varies from 1 to 2, and for nonlinear – from 1 to 3. The influence of measurement errors of one-color radiation temperatures at operating waves on the errors of emissivity determination by nonlinearity equation is established. The metrological advantages of two-color compensative thermometry using the emissivity values, corrected by the nonlinearity equation, are proved. It was found, that at the nonselective distribution of measurement errors of one-color radiation temperatures, measurement errors of the object temperature for two-color compensative, spectral ratio, and energy thermometry are insignificant for technical measurements. Under conditions of selective distribution of measurement errors of one-color radiation temperatures, these errors respectively are 0.04-0.25 %; 1.66-9.30 %; 0.18-0.34 %. For nonlinear emissivity spectral distributions, real for tungsten and iron-carbon alloys, the methodical component due to the nonlinearity doesn’t exceed 0.48 %, which is also acceptable for technical measurements. The method has been developed for practically acceptable conditions of primary pyrometric information obtaining.

Observations of Shoaling Nonlinear Internal Bores across the Central California Inner Shelf

We present observations of shoaling nonlinear internal bores off the coast of central California. The dataset includes 15 moorings deployed during September–October 2017 and cross-shore shipboard surveys. We describe the cross-shore structure and evolution of large-amplitude internal bores as they transit from 9 km (100-m depth) to 1 km offshore (10 m). We observe that two bores arrive each semidiurnal period, both propagating from the southwest; of the total, 72% are tracked to the 10-m isobath. The bore speeds are subtidally modulated, but there is additional bore-to-bore speed variability that is unexplained by the upstream stratification. We quantify temporal and cross-shore variability of the waveguide (the background conditions through which bores propagate) by calculating the linear longwave nonrotating phase speed co and using the nonlinearity coefficient of the Korteweg–de Vries equation α as a metric for stratification. Bore fronts are generally steeper when α is positive and are more rarefied when α is negative, and we observe the bore’s leading edge to rarefy from a steep front when α is positive offshore and negative inshore. High-frequency α fluctuations, such as those nearshore driven by wind relaxations, contribute to bore-to-bore variability of the cross-shore evolution during similar subtidal waveguide conditions. We compare observed bore speeds with co and the rotating group velocities cg, concluding that observed speeds are always faster than cg and are slower than co at depths greater than 32 m and faster than co at depths of less than 32 m. The bores maintain a steady speed while transiting into shallower water, contrary to linear estimates that predict bores to slow.

THERMAL CONTROL OF REACTORS

The article lists the types of reactors: current limiting reactors, smoothing reactor and arc suppression reactor. The principles of electrical energy conversion and methods of compensation of the electric current are described. In addition, the frequency of inspections is established including unplanned, current and capital repairs of equipment. The list is formed of the examined units, as well as the features of thermal imaging diagnostics of reactors with voltages up to and above 1000 V, including the design of a smoothed reactor with a voltage of 780 V and concrete reactor of voltage 10 kV. The thermograms of defects of contact connections are presented. The calculation of the angle dielectric loss tangent tg δ and the steady-state voltage is performed. As a result of the analysis of thermograms, the cause of defects in current limiting reactors with a voltage of 10 kV is formed. On the basis of the calculated value of tg δ, the method of reactor inspection is made; the calculation of the permissible voltage deviation based on the calculated nonlinearity coefficient is carried out. The calculation of the economic damage from the reactor failure depending on the value of the total power, current load and duration of shutdown, as well as the conclusion about the effectiveness of this type of diagnostics are made

Локализованная вторая оптическая гармоника в нелинейно-оптической керамике при фемтосекундном лазерном возбуждении

Second harmonic generation is studied in samples of LiTaO_3 powder ceramics with different lithium concentrations (48.8 and 49.3%) under excitation by a femtosecond laser at a wavelength of 1.026 nm. The dependence of the second harmonic integral power on the incident radiation power is measured, and a method for estimating the nonlinearity coefficient and its homogeneity in green-body ceramics is proposed.

Inhibition grain growth and electrical properties by adding In2O3 to SnO2-Co3O4-Ta2O5 ceramics

In this contribution the effect of In2O3 additions on the microstructure, physical, and electrical properties of the SnO2-Co3O4-Ta2O5 ceramic system was investigated. Since the effect of In2O3 has been studied typically at low levels, special attention has been paid to the effect of high levels (1 and 2 mol % In2O3) in the ceramics. Results show that up to 0.1 mol % In2O3, an increase of indium oxide content is correlated with grain size reduction and an increase of the nonlinearity coefficient (a) and breakdown voltage (EB), producing an augmentation by a factor of 2 in the nonlinearity coefficient and an increment by a factor of 8 in the breakdown voltage. However, shrinkage () and measured density are not influenced by the addition of indium oxide. For samples with 1 and 2 mol % In2O3, in non-calcined condition, In2O3 is present with cubic structure. However, in calcined specimens, In2O3 is not detected anymore and SnO2-crystal structure undergoes a change from tetragonal to cubic. These ceramic samples exhibit high resistivity, behaving like dielectric materials.

Compression of optical similaritons induced by cubic-quintic nonlinear media in a graded-index waveguide

We employ the similarity reductions in two steps to obtain a family of bright and dark similaritons for the variable coefficient cubic–quintic nonlinear Schrödinger equation. Also, parameter domains are delineated in which kink and double-kink similaritons exist for this model. This methodology introduces a free parameter through cubic nonlinearity coefficient which gives us freedom to tune the amplitude and the propagation distance of similaritons in a tapered graded-index waveguide. Furthermore, we observe rapid beam compression of these similaritons for varying detuning parameter and the coefficient of cubic nonlinearity.