Flow and Heat Transfer in Underexpanded Air Jets Issuing from the Sonic Nozzle of a Plasma Generator

We present the results of an experimental investigation and numerical simulation of the gasdynamic structure of underexpanded dissociated-air jets and the heat transfer in these strongly nonequilibrium flows under the test conditions realized in the 100-kW electrodeless VGU-4 plasma generator of the Institute for Problems in Mechanics of the Russian Academy of Sciences (IPM RAS). The flow and heat transfer analysis is carried out on the basis of measurements of the static pressure in the plenum chamber, at the sonic nozzle exit, and on the low-pressure chamber wall, the stagnation pressure on the jet axis using a Pitot tube, and the heat transfer at the stagnation points of water-cooled models placed along the jet axis. The numerical simulation, based on complete Navier-Stokes equations, includes the calculation of (1) equilibrium air plasma flows in the discharge channel of the VGU-4 plasma generator; (2) underexpanded nonequilibrium dissociated-air jet outflow into the ambient space; and (3) axisymmetric jet flow past cylindrical models.     

Ultracompact Fluorescence Lidar Based on a Diode Laser (405 nm, 150 mW) for Remote Sensing of Waterbodies and the Underlying Surface from Unmanned Aerial Vehicles

Doklady Physics - We report on developing an ultracompact (～300 g) fluorescence lidar based on a diode laser (405 nm, 150 mW) and a diffraction spectrometer equipped with a linear photodiode...     

Raman Spectroscopy Diagnostics of the Local Time Profile of an Ultrasound Beam in Water

JETP Letters - It has been demonstrated for the first time that pulsed laser Raman spectroscopy can be used for diagnostics of a local acoustic pressure profile with a peak pressure drop of 50 MPa...     

Concept of the Superpositional State in the Problem of Molecular Mesomorphism: An Analytical Review

It is shown that plastic and liquid crystals differ exclusively in characteristics of topologic order and are peculiar structural forms of more general superpositional state. On the basis of the generalization of the concept of a paracrystal a diagram of structural states is constructed allowing to classify partially ordered phases over the degree of destruction of long-range translational and orientational order.     

Helical disclinations in a cylindrical capillary with nematic liquid crystal

A new type of linear disclinations in a cylindrical capillary with a nematic liquid crystal (NLC) has been studied. It can be considered as a generalized linear disclination of the unit strength. The exact analytical expressions for the elastic field components, lines of force, and the free energy of deformation have been derived.     

Effect of Surface Plasma on Nanosecond Laser Ablation

For the first time, the effect of target surface plasma on nanosecond laser ablation is studied. Surface plasma was generated by a high-power cw fiber laser beam incident on an iron target. A comparison of laser ablation by nanosecond Nd:YAG laser pulses (1064 nm, 5 ns) was performed upon exposure to the cw laser and during its short-term (5 ms) turn off. It was found that the emission intensity twofold increases in the presence of surface plasma. The temperature and electron density of the laser plume induced by the nanosecond laser also increased.     

Coincidence of rotational energy of H<Subscript>2</Subscript>O ortho-para molecules and translation energy near specific temperatures in water and ice

A hypothesis of the quantum nature of the specific temperatures T _s of water and ice, whose values is not random, was formulated. It was found that the quantum energy hΩ _mn of closely located rotational transitions in the ortho and para spin isomers of H₂O molecules coincides with the translation energy kT near the well-known specific temperatures T _s in ice and water. On the basis of this fact it was suggested that ortho-para conversion occurs at temperatures close to T _s upon inelastic collisions and resonance energy exchange kT _s ↔ hΩ _mn in the rotation-translation-rotation (RTR) processes. Such conversion can induce rearrangement of the H-bond set structure and repacking of H₂O molecules. The coincidence kT _s ≈ hΩ _mn was checked for ice and water at 12 known T _s, as well as for heavy water D₂O near T _s = 11.2°C (maximum density) and −140°C (glassy transition). The previously observe strong deformation of the OH Raman band near T _s = 4, 19, 36, and 76°C (maximum density, maximum surface tension, minimum heat capacity, and maximum speed of sound, respectively) was interpreted as a manifestation of the water structure rearrangement induced by H₂O ortho-para conversion.     

High-Frequency (MHz) Ignition of Commercial Flash Lamps for Solid State Lasers

Doklady Physics - A multiple (from 20 to 3 kV) decrease in the ignition threshold of commercial flash lamps for solid-state lasers under HF pumping at a megahertz frequency has been detected. It...     

Lidar observation of the bubble trace in the sea surface layer

The evolutions of the signals of the elastic (Mie) and Raman backscattering of the Nd:YAG laser second-harmonic radiation in the upper layer of the sea under cavitational perturbation induced by the passage of a high-speed boat are compared under the conditions of the outdoor experiment. It is shown that the signal of the elastic scattering on bubbles returns to the background level within the time of ∼10 min. The relaxation time of the spontaneous Raman scattering signal can be an order of magnitude larger than this value (the evaluated value under the particular conditions of this experiment is ∼120 min). Interpretation is given to this difference in attenuation time of the elastic and inelastic scattering signals at the cavitational perturbation of the sea.