Nonstationary periodic spatial waves on the surface of a viscous liquid film falling down a vertical cylinder

The flows of viscous liquid film over the outer surface of a vertical cylinder are examined. Investigation of wave regimes in the case of low flow rates and large cylinder radii is reduced to the analysis of solutions to a nonlinear evolution equation for the film thickness. There are countable numbers of steady-state traveling solution families in the considered model. In turn, most of them are unstable to 2D and 3D perturbations. Thus, evolution of initial perturbations in different ranges of parameter values differs significantly. Some typical scenarios of perturbation development are presented in this work. Initial perturbations with some symmetries, kept in the process of evolution, are of a particular interest. In these cases, solutions are drawn up to the steady-state traveling solutions with similar symmetry.     

The features of rewetting dynamics of the overheated surface by a falling film of cryogenic liquid

The dynamic process of rewetting of the overheated surface by gravitationally falling film of cryogenic liquid was firstly modeled numerically with consideration of local distribution of heat transfer coefficient in the wetting zone along the 2D front. The front shape corresponding to self-organizing regular structures observed in experiments was obtained in the numerical experiment. Evolution of the front shape was studied. It was shown that local motion velocities of different areas of the 2D wetting front differed significantly. Total time of transitional process was determined by the minimal velocity of evaporating liquid boundaries in the front zones between boiling jets. This model allows quantitative determination for the wetting front velocity, variable in time and space, and temperature fields in the heater. Reliability of calculation results was proved by direct comparison with experimental data.     

The nonlinear self-defocusing electromagnetic surface waves in a metalised ferrite film

The dispersion relations for TE s-polarized nonlinear electromagnetic surface waves guided by a metallised ferrite film, surrounded by a nonlinear self-defocusing dielectric cover with intensity dependent refractive indices have been computed. Numerical results are also illustrated to show the propagation characteristics for different values of the film thickness, and at a fixed value of the dielectric-ferrite interface nonlinearity. It has been found that the surface waves exist in both directions of propagation, where the external field is applied. The propagation of these waves is non-reciprocal, and has a resonant interaction in the reverse direction. The power flow carried by the structure has also been calculated for different values of the slab thickness. The non-reciprocity has also been obsorved, and the power flow level can been controlled by the film thickness. of semi-infinite gyromagnetic and nonlinear media². If we increase the operating frequency, the power flow level changes at a fixed film thickness, for 0 and for 0 as in Figs.4. There exist a limited eigenvalues (solutions) with f=17.8GHz for 0, and for different values of the operating frequency for 0. So the eigenvalues and the power flow level can be varied as the operating frequency is tunned. At f=17.8GHz for 0, as in fig.4b, to some value of the power flow there correspond two propagation wave index, which are being related to bistable states of nonlinear surface. All the above mentioned behaviours exhibit the characteristics of microwave switches, isolators, and limiters and could be used in some experimental applications in Microwave Engineering Technology. The other parameters effects as the magnetic field, magnetization, types of ferrite etc. on the dispersion characteristics and the power flow are now under consideration.     

Observation of faraday waves in a Bose-Einstein condensate

Faraday waves in a cigar-shaped Bose-Einstein condensate are created. It is shown that periodically modulating the transverse confinement, and thus the nonlinear interactions in the BEC, excites small amplitude longitudinal oscillations through a parametric resonance. It is also demonstrated that even without the presence of a continuous drive, an initial transverse breathing mode excitation of the condensate leads to spontaneous pattern formation in the longitudinal direction. Finally, the effects of strongly driving the transverse breathing mode with large amplitude are investigated. In this case, impact-oscillator behavior and intriguing nonlinear dynamics, including the gradual emergence of multiple longitudinal modes, are observed.     

Effect of viscosity on thermocapillary breakdown of a falling liquid film

Thermocapillary breakdown of a liquid film flowing due to gravity over a vertical plate with a heater of 150×150 mm is studied in a wide range of liquid properties (in particular, dynamic viscosity at the initial temperature varies from 0.91·10^-3 to 16.9·10^-3 Pa·s) and film Reynolds number (Re = 0.15-53.5). It is found that liquid viscosity has a significant effect on the threshold heat flux corresponding to film breakdown. To take into account the effect of liquid properties, the breakdown criterion traditionally used in literature was modified. This allowed successful generalization of all data obtained.     

Ultrafast dynamics of surface electromagnetic waves in nanohole array on metallic film

We study the ultrafast dynamics of surface electromagnetic waves photogenerated on aluminum film perforated with subwavelength holes array by means of transient photomodulation with ∼100 fs time resolution. We observed a pronounced blueshift of the resonant transmission band that reveals the important role of plasma attenuation in the dynamics and that is inconsistent with plasmon–polariton mechanism of extraordinary transmission. The transient photomodulation spectra were successfully modeled within the Boltzmann equation approach for the electron–phonon relaxation dynamics, involving non-equilibrium hot electrons and quasi-equilibrium phonons.     

Two- and three-dimensional waves in falling film flow in the nonlaminar flow regime: an NMR study

Nuclear magnetic resonance (NMR) velocity-encoded imaging results as well as propagators are presented for the nonlaminar flow regime of falling films. The film is generated by a continuous flow of silicon oil along a vertical poly(methyl methacrylate) plate. While the film remains purely laminar for a film Reynolds number Re_f=0.5, it exhibits laminar-wavy behavior for 1.0≤Re_f≤2.5. In this range, a laminar residual film can be distinguished from averaged waves near the surface of the film from measurements of the flow velocity ν₂ along the direction of gravity as a function of the coordinatex normal to the plate. The perpendicular velocity components, ν _x and ν _y are zero within the accuracy of the measurement, indicating that the wave motion is two-dimensional in the laminar-wavy case. For higher Re_f the waves are found to be three-dimensional, a straightforward division into a residual film and waves in ν _z is lost and the waves extend over the whole thickness of the film.     

Nondestructive determination of film thickness with laser-induced surface acoustic waves

The application of surface acoustic waves(SAWs) for thickness measurement is presented. By studying the impact of film thickness h on the dispersion phenomenon of surface acoustic waves, a method for thickness determination based on theoretical dispersion curve v( fh) and experimental dispersion curve v( f) is developed. The method provides a series of thickness values at different frequencies f, and the mean value is considered as the final result of the measurement. The thicknesses of six interconnect films are determined by SAWs, and the results are compared with the manufacturer's data.The relative differences are in the range from 0.4% to 2.18%, which indicates that the surface acoustic wave technique is reliable and accurate in the nondestructive thickness determination for films. This method can be generally used for fast and direct determination of film thickness.     

Thermocapillary waves in a liquid film

This paper investigates two-dimensional waves in a heated liquid film in the presence of the thermocapillary effect. The waves in the film are described using the integral model. The first part of the paper considers film instability for cases of fixed temperature of the plate and fixed heat flux in the plate. The liquid temperature disturbance is calculated from the energy equation for arbitrary values of Peclet number. In the second part, the evolution of waves in a heated film is modeled based on the system of equations for film thickness, flow rate, and the energy equation. In numerical modeling of the wave evolution, the boundary of the region of growing disturbances agrees well with results of stability analysis. The calculations show that for a vertical film the thermocapillary effect leads to broadening of the instability region only at low Peclet numbers.     

Modeling of wave regimes on the film of viscous liquid falling down a vertical plate

Evolution of disturbances on the surface of liquid film falling free over a vertical plane is considered. In the case of low Reynolds numbers, the problem is reduced to investigation of a single equation describing evolution of film thickness disturbances. With the use of information about the structure of the family of steady-state traveling solutions to this equation, the typical scenarios of evolution for periodic disturbances were identified.     

Influence of roughness on the detection of mechanical characteristics of low-k film by the surface acoustic waves

The surface acoustic wave （SAW） technique is a precise and nondestructive method to detect the mechanical charac- teristics of the thin low dielectric constant （low-k） film by matching the theoretical dispersion curve with the experimental dispersion curve. In this paper, the influence of sample roughness on the precision of SAW mechanical detection is inves- tigated in detail. Random roughness values at the surface of low-k film and at the interface between this low-k film and the substrate are obtained by the Monte Carlo method. The dispersive characteristic of SAW on the layered structure with rough surface and rough interface is modeled by numerical simulation of finite element method. The Young＇s moduli of the Black DiamondTM samples with different roughness values are determined by SAWs in the experiment. The results show that the influence of sample roughness is very small when the root-mean-square （RMS） of roughness is smaller than 50 nm and correlation length is smaller than 20 μm. This study indicates that the SAW technique is reliable and precise in the nondestructive mechanical detection for low-k films.     

Study of the sorption processes in a piezoelectric-molecularly imprinted polymer film structure using Rayleigh surface acoustic waves

The sorption processes in a piezoelectric-molecularly imprinted polymer film structure, where the polymer is synthesized from the monomers of bisphenol-A glycerolate diacrylate using imprinted morpholine molecules as template molecules, are experimentally studied with Rayleigh surface acoustic waves at a frequency of 120 MHz. The desorption processes for morpholine are found to be anomalously slow as compared to other analytes under study. The possibility of the application of the results obtained for creating selective chemical sensors based on surface acoustic waves is discussed.