Ignition of a vapor-gas mixture by a moving small-size source

A theoretical analysis of the ignition of a liquid fuel vapor-air mixture by a moving small source of heating was performed. A gas-phase model of the ignition with consideration given to heat transfer, liquid fuel evaporation, diffusion and convective motion of fuel vapor in the oxidizer medium, crystallization of the heating source, kinetics of the vaporization and ignition processes, temperature dependence of the thermophysical characteristics of the interacting substances, and character of motion of the heating source in the vapor-gas mixture was developed. The values of the ignition delay time τ _d , the main characteristic of the process, were determined. It was established how τ _d depends on the initial temperature, heating source sizes, velocity and trajectory of the heating source, and ambient air temperature.     

Fast electro-optical response of a cell with a homeoplanar layer of a nematic liquid crystal

The refraction of light, i.e., the turn of an extraordinary ray in the liquid crystal layer similar to total internal reflection at an interface between two media, has been studied in a cell with the homeoplanar orientation of the director. The rise, τ_on, and decay, τ_off, times of optical responses have been obtained for various angles of incidence of light on a liquid crystal layer subjected to an electric field. The times τ_on and τ_off of optical responses for the angles of incidence much larger than the angle of total internal reflection are 1–2 ms, which is three orders of magnitude smaller than the relaxation time of an optical response in the case of normal incidence of the ray.     

Stability of a dry patch in a viscous flowing film

We investigate the dewetting of liquid films flowing down an incline. At low flow rate we observe the formation of stationary dry patches edged with a liquid rim. Their shape can be predicted by a simple model in which the rim weight is balanced by surface tension. Above a critical flow rate per unit length Γ_c of typical scale U_cl_c (U_c capillary velocity, l_c capillary length), these dry patches cannot remain stationary and are swept away. An improved model taking into account capillary effects linked to contact line curvature, hydrostatic pressure in the film and inertial effects predicts this loss of stability in good agreement with experiments for sufficiently high viscosity values.     

液态三元Ni-Cu-Fe合金比热的实验与计算研究

采用电磁悬浮落滴式量热方法测定了液态三元Ni₆₀Cu₂₀Fe₂₀合金在1436—2008K温度范围内的比热,实验获得的最大过冷度达232K(0.14T_L),结果表明比热值为33.27J·mol^-1·K^-1,并且随温度变化很小.在实验基础上,根据分子动力学方法结合嵌入原子势(EAM)和Quantum Sutton-Chen多体势(QSC)对比热进行了理论计算,揭示 关键词： 液态合金 比热 电磁悬浮 分子动力学计算     

Sonochemical production of a carbon nanotube

Sonochemical production of a carbon nanotube has been studied. The carbon nanotube is produced by applying ultrasound to liquid chlorobenzene with ZnCl₂ particles and to o-dichlorobenzene with ZnCl₂ and Zn particles. It is considered that the polymer and the disordered carbon, which are formed by cavitational collapse in homogeneous liquid, are annealed by the inter-particle collision induced by the turbulent flow and shockwaves.     

First observation of ferromagnetism and ferromagnetic domains in a liquid metal

80 Pd₂₀ alloy below the Curie temperature T_C(l)=1257 K of the liquid state. The magnetization of the undercooled liquid sample has been measured as a function of temperature using a modified Faraday balance. Below T_C(l), the magnetization of the liquid metal shows a plateau in the weak external field of μ₀H_z=5.6 mT. The effect is comparable to the behaviour of the corresponding solid phase, indicating the onset of spontaneous magnetization with ferromagnetic domains. T_C(l) is about 20 K lower than the Curie temperature of the solid phase T_C(s). Received: 24 February 1997/Accepted: 16 May 1997     

The effects of external applied voltage on the nonlinear refractive index and the birefringence of a dye-doped nematic mixture

The nonlinear refractive index, n₂, and the birefringence, Δn, of a nematic liquid crystal mixture (denoted as 1294-1b) doped with a anthraquinone derivative (denoted as AQ) dye were measured as a function of an external ac applied voltage. The self-phased modulation effect was used to measure the nonlinear refractive index of homeotropical-aligned samples. The change of the dyed liquid crystal nonlinearity, which is the direct impact of the applied voltage on the dye molecules orientation, was not observed for the nonlinear response of the pure liquid crystal. Planar (homogeneous) aligned samples were used for birefringence measurements by taking into account the absorption coefficients of the dye. The birefringence decreased to a limiting value in the high voltage region for both pure and dye-doped samples, although in the presence of the absorbing dye the birefringence of the liquid crystal was not approximately changed.The polarized absorption spectra of the dye in nematic mixture were recorded in parallel-aligned liquid crystal cell and its dichroic ratio R and the order parameter S_d were obtained. The electro-optical effect of the guest-host system was also using polarized spectroscopic method.     

Statistic characteristics of the gas-liquid flow in a vertical minichannel

The gas-liquid upward flow was studied in a rectangular minichannel of 1.75×3.8 mm and length of 0.7 m. The experiments were carried out within the range of the gas superficial velocity from 0.1 to 10 m/s and the liquid superficial velocity from 0.07 to 0.7 m/s for the co-current H₂O/CO₂ flow under the conditions of saturation. The method for the two-beam laser scanning of structure and determination of statistic characteristics of the two-phase flow was worked through. The slug-bubble, slug, transitional, churn, and annular flows were distinguished. The statistics characteristics of liquid and gas phases motion in a minichannel were obtained for the first time including the velocities of phase motion.     

Properties of the adsorption layer in a binary liquid mixture near the critical point

A method for the determination of parameters of the surface layer (thickness and refraction index) at the liquid-vapor interface in binary liquid mixtures was developed. The parameters of the surface layer for the C₇H₁₄-C₇F₁₄ liquid mixture in the vicinity of the critical point, which was studied by means of ellipsometry in [1], were calculated using the proposed method. The temperature dependences of the thickness and refraction index that were determined in the homogeneous isotropic layer approximation at the interface liquid-vapor, show structural peculiarities that were not observed earlier. Their appearance is explained by the possible influence of hydrodynamic processes at the boundary.     

Stability of a bubble in a dielectric liquid in an external electrostatic field

Critical instability conditions are found for a gas bubble in a liquid dielectric in a uniform external electrostatic field E ₀. It is shown that they depend both on the magnitude of E ₀ and on the properties of the liquid, as well as on the gas pressure in the bubble. In a linear approximation with respect to the square of the eccentricity of an equilibrium spheroidal form, the equilibrium eccentricity of the bubble exceeds the equilibrium eccentricity of a drop in the field E ₀. The gas pressure in the bubble lowers the critical electric field E ₀ for development of an instability in the bubble. Zh. Tekh. Fiz. 69, 43–48 (August 1999)     

Feasibility Study of Delay-Line Localization in a Mini-PET Scanner

The concept of delay-line localization for a Mini-PET scanner is described. The time resolution of small BaF₂ scintillators mounted on quartz as well as liquid light guides of various lengths was measured with ²²Na versus a large BaF₂. It seems feasible to construct a Mini-PET scanner with optical delay-line localization. This revised version was published online in September 2006 with corrections to the Cover Date.     

Stabilization of electron-hole liquid in uniaxially strained germanium in a strong magnetic field

Luminescence spectra of uniaxially and uniformly strained high-purity germanium crystals at liquid-helium temperatures in a magnetic field of up to 14 T have been investigated. In strongly strained Ge crystals, a new line has been detected on the low-energy side of the excitonline in magnetic fields higher than 4 T. Studies of this line’s characteristics as functions of pressure, temperature, and magnetic field have led us to conclude that its presence is due to recombination of electron-hole pairs in an electron-hole liquid. The experimental data suggest that the metallic electron-hole liquid is stabilized in a strong magnetic field. By approximating the shape of the newly detected line using the model of metallic electron-hole liquid, we have obtained the electron-hole liquid density n _EHL(B) and Fermi energies E _Fe,h of electrons and holes. The liquid binding energy ø as a function of magnetic field has been estimated.     

Thermocapillary self-focusing of a laser beam: A theoretical analysis

A gaussian laser beam reflected from a thermocapillary liquid surface self-focuses at a distance L from the sample surface at a time-instant t_s after the beginning of the irradiation. The theoretical relation t_s(L) is calculated as a function of the liquid physical properties and the laser power.     

Scattering and amplification of light in a layer of a nematic liquid crystal

The role of light scattering in liquid crystal lasers can be of two kinds. It can induce undesirable losses increasing the lasing threshold or it can promote the appearance of feedback necessary for lasing. The light amplification spectra of the liquid crystal in the isotropic and light-scattering nematic phases have been measured. For comparison, at a close pump power, the amplification spectra have been measured on a TiO₂ nanoparticle suspension in an isotropic solvent, where the mean free path of photons is the same as that in the liquid crystal. The amplifications in two systems are significantly different, because the shapes of their scattering patterns are strongly different.     

Molecular dynamics simulations of a flexible liquid crystal

Molecular dynamics simulations have been performed for a liquid crystal composed of a Gay—Berne core site with two alkyl chains of different length (C₇ and C₃) at either end of the molecule. Calculations have been carried out for 512 molecules in the NVT ensemble for simulation times of up to 8.0ns at two distinct densities. The liquid crystal phases of the material have been fully characterized by measurements of orientational order parameters and radial distribution functions in each phase. Results are also presented for conformational distributions and effective torsional potentials of the system. We conclude that models of this nature represent a powerful approach to the study of flexibility in mesogenic systems and open up possibilities for predicting both the phase behaviour and bulk properties of liquid crystals based solely on a prior knowledge of intermolecular interactions.     

Application of a radioactive tracer method for diffusion study in some liquids

In this paper a radioactive tracer technique based on sliding cell method developed in our laboratory for the study of diffusion in liquids is presented in detail. This method consists of radioactive and non-radioactive liquid columns of equal length and the radiation detector is placed in a vertical geometry over the diffusion column. Some liquid metals and aqueous electrolyte solutions were studied by this method. The data of liquid metals like mercury and gallium have been analyzed from the point of view of hard sphere model and those of electrolyte solutions from phenomenological theories. Onsager’s coefficientsL ₁₁,L ₁₂,L ₂₂ have been calculated from the experimental data and the variation of diffusion with solute concentration has been explained from ion-ion interaction.     

Spray generator of singlet oxygen for a chemical oxygen-iodine laser

A spray type of singlet oxygen generator for driving the Chemical Oxygen-Iodine Laser was developed. Singlet oxygen, O₂(¹Δ_g), is generated by a fast reaction of chlorine with basic hydrogen peroxide solution in the form of a dense spray. A mathematical model of this reaction system showed that O₂(¹Δ_g) can be generated in this system with a high yield (0.70–0.80), high utilization of chlorine (0.75–0.95), and effective utilization of liquid (0.36–0.54) at very high generator pressures (35–75 kPa). Experimental studies of this reaction system without an efficient separation of liquid proved an efficient O₂(¹Δ_g) production characterized by a rather high product of chlorine utilization and O₂(¹Δ_g) yield (0.4–0.9) at very high generator pressures (30–80 kPa). This pressure is much higher than the operation pressure used in other generators, which should be beneficial for a pressure recovery system of the COIL. These results provided the basis for designing a centrifugal spray generator with an efficient separation of liquid from the gas flow, which is the subject of the following paper.     

On a study of the superposition effect of diffracted X-rays by a liquid column and the optimum thickness for X-ray diffraction

A measure of intensity due to the superposition of diffracted X-rays from elementary regions in the line of X-ray path has been calculated on the basis of Gaussian distribution of intensity from every element. This gives the optimum thickness for maximum intensity implicitly by the relation. Μt₀=α?′(αt₀)/?(αt₀) where ? is the error integral and α is a characteristic of the liquid which determines the Gaussian distribution form for the particular liquid. Good agreement between the theoretical relations and the experimental values have been observed.     

Investigation of the dynamics of a percolation transition under rapid compression of a nanoporous body-nonwetting liquid system

The dynamics of infiltration of a nanoporous body with a nonwetting liquid under rapid compression is studied experimentally and theoretically. Experiments are carried out on systems formed by a hydrophobic nanoporous body Libersorb 23, water, and an aqueous solution of CaCl₂ at a compression rate of \(\dot p\) ≥ 10⁴ atm/s. It is found that the infiltration begins and occurs at a new constant pressure independent of the compression energy and viscosity of the liquid. The time of infiltration and the filled volume increase with the compression energy. A model of infiltration of a nanoporous body with a nonwetting liquid is constructed; using this model, infiltration is described as a spatially nonuniform process with the help of distribution functions for clusters formed by pores accessible to infiltration and filled ones. On the basis of the proposed system of kinetic equations for these distribution functions, it is shown that under rapid compression, the infiltration process must occur at a constant pressure p _c whose value is controlled by a new infiltration threshold θ _c = 0.28 for the fraction of accessible pores, which is higher than percolation threshold θ _c0 = 0.18. Quantity θ _c is a universal characteristic of porous bodies. In the range θ _c0 < θ < θ _c , infiltration of the porous body should not be observed. It is shown that the solution to the system of kinetic equations leads to a nonlinear response by the medium to an external action (rapid compression), which means the compensation of this action by percolation of the liquid from clusters of filled pores of finite size to an infinitely large cluster of accessible but unfilled pores. As a result of such compensation, infiltration is independent of the viscosity of the liquid. It is found that all experimental results can be described quantitatively in the proposed model.     

Formation,growth and ageing of clathrate hydrate crystals in a porous medium

An experimental study was performed to visually observe the driving force dependence of hydrate growth in a porous medium filled with either liquid water and dissolved CO₂ or liquid water and gaseous CO₂. The given system subcooling, ΔT _sub, i.e. the deficiency of the system temperature from the triple CO₂?hydrate?water equilibrium temperature under a given pressure, ranged from 1.7?K to 7.3?K. The fine dendrites initially formed at ΔT _sub?=?7.3?K changed quickly into particulate crystals. For ΔT _sub?=?1.7?K, faceted hydrate crystals grew and the subsequent morphological change was hardly identified for an eight-day observation period. These results indicate that the physical bonding between hydrate crystals and skeletal materials becomes stronger with decreasing driving force, suggesting that the fluid dynamic and mechanical properties of hydrate-bearing sediments vary depending on the hydrate crystal growth process.