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This paper presents a numerical and experimental study on hydrodynamic behavior of thin liquid films in rectangular domains. Three-dimensional computer simulations were performed using the lattice Boltzmann equation method (LBM). The liquid films laying on solid and liquid substrates are considered. The rupture of liquid films in computations is initiated via the thermocapillary (Marangoni) effect by applying an initial spatially localized temperature perturbation. The rupture scenario is found to depend on the shape of the temperature distribution and on the wettability of the solid substrate. For a wettable solid substrate, complete rupture does not occur: a residual thin liquid film remains at the substrate in the region of pseudo-rupture. For a non-wettable solid substrate, a sharp-peaked axisymmetric temperature distribution induces the rupture at the center of symmetry where the temperature is maximal. Axisymmetric temperature distribution with a flat-peaked temperature profile initiates rupture of the liquid film along a circle at some distance from the center of symmetry. The outer boundary of the rupture expands, while the inner liquid disk transforms into a toroidal figure and ultimately into an oscillating droplet.
We also apply the LBM to simulations of an evolution of one or two holes in liquid films for two-layer systems of immiscible fluids in a rectangular cell. The computed patterns are successfully compared against the results of experimental visualizations. Both the experiments and the simulations demonstrate that the initially circular holes evolved in the rectangular cell undergoing drastic changes of their shape under the effects of the surface tension and gravity. In the case of two interacting holes, the disruption of the liquid bridge separating two holes is experimentally observed and numerically simulated.
In this work, we report on local ferroelectric and piezoelectric properties of nanostructured polymer composites P(VDF-TrFE)+x(Ba,Pb)(Zr,Ti)O3 (x = 0 - 50 %). High-resolution imaging of ferroelectric domains, local polarization switching, and polarization relaxation dynamics were studied by piezoresponse force microscopy. In particular, we found that (Ba,Pb)(Zr,Ti)O3 inclusions usually show a strong unipolar piezoresponse signal, as compared to the polymer matrix. By scanning under high dc voltage the films can be polarized uniformly under both positive and negative electric fields. Stability of the polarized state is discussed.
An experimental and theoretical investigation of the air trapping by a blunt, locally spherical body impacting onto the free surface of water is conducted. In the parameter regime previously studied theoretically by Hicks & Purvis (J. Fluid Mech., vol. 649, 2010, pp. 135–163), excellent agreement between experimental data and theoretical modelling is obtained. Earlier predictions of the radius of the trapped air pocket are confirmed. A boundary element method is used to consider air cushioning of an impact of an axisymmetric body into water. Efficient computational methods are obtained by analytically integrating the boundary integral equation over the azimuthal variable. The resulting numerically computed free-surface profiles predict an annular touchdown region in excellent agreement with the experiments.
The International Astronomy Olympiad (IAO) was founded in the 1990s as an annual scientific educating event for students of the junior high school classes. Starting from 4 teams at the 1st event in 1996 the Olympiad includes more than 20 countries nowadays. The style of the problems of IAO is aimed at developing the imagination, creativity and independent thinking. They stimulate the students to recognize the problem independently, to choose a model, to make necessary suppositions, estimations, to conduct multiway calculations or logic operations. The Asian-Pacific Astronomy Olympiad was founded as a “daughter” (“affiliated”) olympiad in system of the International Astronomy Olympiad in 2005.
The emergency response and radiation monitoring system in the Murmansk region established by request of the Murmansk region Government was developed by the Energy Safety Analysis Center of Nuclear Safety Institute of the Russian Academy of Sciences (IBRAE RAS) in 2005–2007 under a special project. The system meets all actual international and domestic requirements and may be used as a prototype in similar projects.
This paper presents an experimental study of internal waves generated by circular and rectilinear oscillations of a circular cylinder in a uniformly stratified fluid. The synthetic schlieren technique is used for quantitative analysis of the internal-wave parameters. It is shown that at small oscillation amplitudes, the wave pattern observed for circular oscillations is in good agreement with linear theory: internal waves are radiated in the wave beams passing through the first and third quadrants of a Cartesian coordinate system for the clockwise direction of the cylinder motion, and the intensity of these waves is twice the intensity measured for ‘St Andrew's cross’ waves generated by purely horizontal or vertical oscillations of the same frequency and amplitude. As the amplitude of circular oscillations increases, significant nonlinear effects are observed: (i) a strong density-gradient ‘zero-frequency’ disturbance is generated, and (ii) a region of intense fluid stirring is formed around the cylinder serving as an additional dissipative mechanism that changes the shape of wave envelopes and decreases the intensity of wave motions. In the same range of oscillation amplitudes, the wave generation by rectilinear (horizontal and vertical) oscillations is shown to be by and large a linear process, with moderate manifestations of nonlinearity such as weak ‘zero-frequency’ disturbance and weak variation of the shape of wave envelopes with the oscillation amplitude. Analysis of spatiotemporal images reveals different scenarios of transient effects in the cases of circular and rectilinear oscillations. In general, circular oscillations tend to generate disturbances evolving at longer time scales.
This paper presents an experimental study on the propagation speed of gravity currents at moderate values of a gravity Reynolds number. Two cases are considered: gravity currents propagating along a rigid boundary and intrusive gravity currents. For the first case, a semi-empirical formula for the front propagation speed derived from simple energy arguments is shown to capture well the effect of flow deceleration because of viscous dissipation. In the second case, the propagation speed is shown to agree with the one predicted for energy-conserving virtually inviscid flows (Shin, Dalziel & Linden, J. Fluid Mech. vol. 521, 2004, p. 1), which implies that the losses due to vorticity generation and mixing at the liquid–liquid interface play only a minor role in the total balance of energy.
In this paper the experimental study presented in Part 1 is extended to the three-dimensional case. The in-line force coefficients (added mass and damping) of a sphere oscillating horizontally in a uniformly stratified fluid of limited depth and in a smooth pycnocline are evaluated from Fourier-transforms of the experimental records of impulse response functions. The hydrodynamic loads in the three- and two-dimensional cases are shown to be essentially different, notably in the low-frequency limit, where the damping in the three-dimensional case is zero, while in the two-dimensional case it is maximized due to phenomena akin to blocking. The generalization of the experimental results for affinely similar geometries is discussed. It is found that, as the characteristic vertical extent of stratification decreases, the mean power of internal waves radiated by the oscillating sphere reduces and the maximum of the frequency spectrum of wave power shifts toward lower frequency, which is qualitatively similar to the effects observed in the two-dimensional case. Physically, horizontal stratified waveguides act as low-pass filters since internal waves with nearly vertical group-velocity vector cannot be effectively radiated from oscillating bodies.
This paper presents the force coefficients (added mass and damping) for a circular
cylinder oscillating horizontally in a uniformly stratified fluid of limited depth and
in a continuously stratified fluid with a smooth pycnocline. The frequency-dependent
added mass and damping are evaluated from Fourier transforms of the experimental
records of impulse response functions. The stratification is shown to have a strong
effect on the fluid–body interaction. It is found that, when the characteristic vertical
extent of stratification (depth of uniformly stratified fluid or pycnocline thickness)
decreases, the power radiated with internal waves is reduced and the maximum of
the frequency spectrum of wave power shifts toward lower frequency. The results of
experiments are compared with available theoretical predictions.
Results of ion implantation of nitrogen into electrodeposited hard chromium and pure aluminum by a high-dose ion-beam source are presented and compared to plasma-source ion implantation. The large-area, high current density ion-beam source can be characterized, with respect to surface modification use, by a uniform emitted dose rate in the range of 1016 to 5 × 1017 N cm−2 min−1 over an area of <100 cm2 and with acceleration energies of 10–50 keV. The implantation range and retained dose (measured using ion-beam analysis), the surface hardness, coefficient of friction, and the change in the wear coefficient (measured by nanohardness indentation and pin-on-disk wear testing) that were obtained with an applied dose rate of ∼1.7 × 1017 N cm−2 min−1 at 25 kV are given, and they are compared to results obtained with plasma-source ion implantation.
Ion implantation experiments of C, N and O into stainless steel have been performed with beam-line and plasma source ion implantation methods. Acceleration voltages are varied between 27 and 50 kV, with pulsed ion current densities between 1 and 10 mA/cm2. Implanted doses range from 0.5 to 3×1018cm-2, while workpiece temperatures are maintained between 25 and 800°C. The implant concentration profiles, microstructure and surface mechanical properties of the implanted materials are reported.
The present review is of the experimental investigations on laser-plasma interaction being carried out in past years at IAE. Experiments were conducted on the “Mishen” facility. The laser system of Mishen consists of two channels with output beam parameters as follows: the main beam—output energy 100–200 J (λ = 1.054 μm) in 3-ns pulse, divergence ∼2 × 10-4 rad, contrast ratio ∼106, power density at the target surface ∼1013–1014 W/cm2; the diagnostic beam–output energy 10–20 J (λ = 1.054 μm) and 5–10 J (λ = 0.53 μm) in 0.3-ns pulse, divergence ∼10-4 rad, power density 1013 - 1014 W/cm2. Our aim in this experiment is to study the different aspects of the ICF processes in flat geometry. The main issues of our studies are hydrodynamic aspects, including acceleration efficiency, high-velocity impact in cascade targets, hydrostability, and X-ray physicsconversion efficiency, heat transfer, and X-ray-driven targets.
The article reviews experiments on flash X radiography of laser-accelerated foils. The spatial resolution, sensitivity, spectral range, and signal-to-noise ratio of measurements were carefully optimized and characterized. The method was used at the Mishen facility to measure a distribution of mass ablative rate across the focal spot and for observation of the transverse plasma flows during the drive laser pulse.
X-ray emission from planar targets irradiated by 1.054-μm laser pulses was observed with temporal, spatial, and spectral resolution. The main purpose of these measurements was the investigation of energy transfer in multilayer targets and X-ray conversion efficiency. A mass ablation rate was determined from temporal analysis of multicharged ion line emission and a key role of corona X-ray emission in accelerated material preheating was established.
The acceleration of electrons in a laser plasma at the densities below the critical one is investigated by a particle simulation. It is shown that the stabilization of parametric instability and limitation of the energies of the accelerated electrons take place. The structure of the plasma electron distribution function is examined.
Experimental studies of the ablative acceleration of thin foils as carried out on the “Mishen” device (Nd laser, λ = 1·06μm, 3 nsec pulses) are reported. The plasma corona in the range of power densities 1013–1014 W/cm2 is shown to absorb 80–90% of the laser beam energy, the classical collisional absorption mechanism being the main one. Jet-like and filamentary structures are observed in the laser-plasma interaction; however, the main plasma parameters are found to be independent of the presence (or absence) of such structures. The measured hydrodynamic efficiency of stable ablative acceleration in plane geometry is ≲5%. The production of high-speed cumulative jets with irradiated thin-wall hollow conical targets is reported as an example of a non-traditional ablative acceleration geometry.
The geometrical shape of the Moon is determined from measurements of absolute heights of the lunar surface, while its dynamical shape is described by means of the Moon's gravity field parameters. All these data are derived from observations of the lunar artificial satellites (‘Luna-10’, ‘Orbiters 1-4’) and astronomical measurements.
In the paper differences of the lunar geometrical and dynamical figures are analysed. It is shown, that the homogeneous model of the Moon is not capable of explaining these differences. It is found, that the lunar centre of gravity situated about 0.9 km to the north, and 1.1 km nearer to the Earth, than the centre of its geometrical figure.