Modeling radiation characteristics of semitransparent media containing bubbles or particles

Modeling of radiation characteristics of semitransparent media containing particles or bubbles in the independent scattering limit is examined. The existing radiative properties models of a single particle in an absorbing medium using the approaches based on (1) the classical Mie theory neglecting absorption by the matrix, (2) the far field approximation, and (3) the near field approximation are reviewed. Comparison between models and experimental measurements are carried out not only for the radiation characteristics but also for hemispherical transmittance and reflectance of porous fused quartz. Large differences are found among the three models predicting the bubble radiative properties when the matrix is strongly absorbing and/or the bubbles are optically large. However, these disagreements are masked by the matrix absorption during calculation of radiation characteristics of the participating medium. It is shown that all three approaches can be used for radiative transfer calculations in an absorbing matrix containing bubbles.     

Angle-resolved reflectance of obliquely aligned silver nanorods

Arrays of silver nanorods (AgNRs) formed by oblique-angle deposition (OAD) are strongly anisotropic, with either metallic or dielectric characteristics depending on the polarization of incident light, and may be used to enhance Raman scattering and surface plasmon polaritons. This work investigates the polarization-dependent reflectance of inclined AgNR arrays at the wavelengths of 635 and 977 nm. The specular reflectance at various incidence angles and the bidirectional reflectance distribution function were measured with a laser scatterometer, while the directional-hemispherical reflectance was measured with an integrating sphere. The AgNR layer is modeled as an effectively homogenous, optically uniaxial material using the effective medium theory to elucidate the dielectric or metallic response for differently polarized incidence. The thin-film optics formulation is modified considering optical anisotropy and surface scattering. This study helps gain a better understanding of optical properties of nanostructured materials.     

Measurements of radiation characteristics of fused quartz containing bubbles

We report experimental measurement of radiation characteristics of fused quartz containing bubbles over the spectral region from 1.67 to 3.5 microm. The radiation characteristics were retrieved by an inverse method that minimizes the quadratic difference between the measured and the calculated spectral bidirectional transmittance and reflectance for different sample thicknesses. The theoretical spectral transmittances and reflectances were computed by solving the one-dimensional radiative transfer equation by the discrete-ordinates method for a nonemitting, homogeneous, and scattering medium. The results of the inversion were shown to be independent of the sample thickness for samples thicker than 3 mm and clearly demonstrate that bubbles have an effect on the radiation characteristics of fused quartz.     

Spc of a near zero-defect process subject to random shocks

In this paper we study the problem of monitoring and control of a type of process in which long series with no non-conformities are observed together with occasional samples containing a large number of non-conformities. We call this a near zero-defect process subject to random shocks. Such processes occur often in practice, and a model is proposed for the identification of real non-random variations of process characteristics. Based on the statistical analysis carried out for this model, a procedure for decision-making in the control of this type of process is suggested, and analysis of some actual cases presented.     

Properties of Electron Bubbles in Liquid Helium

We present calculations of a number of properties of electron bubbles in liquid helium. The size and shape of bubbles containing electrons in different quantum states is determined based on a simplified model. We then find how the geometry of these bubbles changes with the applied pressure. The radiative lifetime of bubbles with electrons in excited states is calculated. Finally, we use a quantum Monte Carlo method to determine the properties of a bubble containing two electrons. We show that this object is unstable against fission.     

Efficiency factors and radiation characteristics of spherical scatterers in an absorbing medium

The radiative properties of bubbles or particles embedded in an absorbing medium are investigated. We aim first to determine the conditions under which absorption by the surrounding medium must be accounted for in the calculation of the efficiency factors by comparing results from Mie theory and the far-field and near-field approximations. Then, we relate these approximations for a single particle to the effective radiation characteristics required for solving the radiative transfer in an ensemble of scatterers embedded in an absorbing medium. The results indicate that the efficiency factors for a spherical particle can differ significantly from one model to another, in particular for large particle size parameter and matrix absorption index. Moreover, the effective scattering coefficient should be expressed based on the far-field approximation. Also, the choice of the absorption efficiency factor depends on the model used for estimating the effective absorption coefficient. However, for small void fractions, absorption by the matrix dominates, and models for the absorption coefficient and efficiency factor are unimportant. Finally, for bubbles in water, the conventional Mie theory can be used between 0.2 and 200 mum except at some wavelengths at which absorption by water must be accounted for.     

Interaction of the acoustic signal with motionless discretely layered medium containing a layer of bubbly liquid

The dynamics of the pulse perturbation of the low-amplitude pressure in the motionless discretely layered medium containing a layer of liquid with polydisperse gas bubbles has been studied theoretically. Theoretical method basics of the calculation of the acoustic signal distortion during the diagnostics of multilayer samples containing a layer of bubbly liquid are presented. It is shown that specific dispersion and dissipative properties of the layer of bubbly liquid can affect considerably the dynamics of the acoustic signal in the multilayer medium as a function of the main frequency of the signal. The theoretical models of the dynamics of multiphase media can be verified using this method. It was established that it is possible to use this theory for the calculation of the acoustic signal distortion at its interaction with multilayer objects containing the layer of bubbly liquid.     

Parametric modeling and estimation of acoustic sediment propertiesusing a system identification approach

The acoustic properties of marine sediments are measured to obtain an acoustic signature of their mechanical characteristics. The proposed 1-D wave propagation model accounts for absorption and dispersion. Use is made of an inverse procedure based on a maximum likelihood estimator for obtaining a parametric identification of the sediments. Measurements are performed in the laboratory, in reflection and transmission modes, on prepared samples of natural sediments, at normal incidence, and using a controlled measurement environment in the frequency range of 300 to 700 kHz. The model validation is performed for a water layer, an ideal medium with little absorption and dispersion, and for a silty-clay layer. A comparison between the estimated and measured amplitude and phase characteristics for these two media indicates that the parametric identification of the silty-clay is successful. For both media, comparable differences, of 0.3 dB maximum for the amplitude and three degrees for the phase, are observed     

The Effect of Gas Properties on Bubble Formation,Growth, and Detachment

Bubble formation and growth play an important role in various processes and industries, where the dispersion of gas bubbles in a liquid medium occurs frequently. In this paper, the formation, growth, and detachment of gas bubbles produced from a submerged needle in water are numerically and experimentally investigated. The effect of injected gas properties on bubble characteristics, including bubble diameter, contact angle, and the frequency of bubble formation, is evaluated. In particular, the changes in bubble characteristics during the injection process are investigated for three different gases to evaluate the effect of density and surface tension on the bubble detachment criteria. The present numerical results show an acceptable agreement with experiments under different operating conditions. The results show that the increase in surface tension, and the decrease in gas density result in larger bubble sizes before detachment occurs. Moreover, the bubble generation frequency is found to strongly depend on the contact angle and the surface tension.     

Application of the embedded atom model to liquid metals: Liquid mercury

The procedure is suggested for the calculation of the embedded atom potential for a liquid metal, which involves the use of diffraction data on the structure of material in the vicinity of the melting point. The procedure is used for mercury at temperatures from 293 to 1803 K. The data on the structure of mercury at 293 K and the thermodynamic properties of mercury at 293 and 1673 K are used in selecting the parameters of embedded atom potential. The calculated critical temperature for mercury is close to the actual value of ～1750 K. The self-diffusion coefficients increase with temperature by the power law. The variation of the structure characteristics of liquid metal with the temperature increasing by several hundred degrees is described correctly. However, at temperatures above 1000 K, the predicted structure of models differs appreciably from the actual structure. These differences are explained by the dependence of the real potential of interparticle interaction of mercury on density during the metal-nonmetal transition occurring in the case of heating.     

Glass-metal particulate composites

Oxide glasses containing ultrafine metal particles have interesting physical properties and have been widely used in practical systems. The various preparational techniques developed so far for making these materials are discussed. Electrical conduction in these composites is controlled by electron tunnelling between the metal islands. At high electric fields certain glasses containing bismuth granules show a memory switching effect. The latter has been explained by a particle stretching model. Optical absorption characteristics of these composites can be explained on the basis of various effective medium theories developed so far for inhomogeneous materials. Glasses containing ferromagnetic metal grains show a superparamagnetic behaviour with a transition temperature below 300 K. Improvement in the mechanical properties of glasses can be achieved by incorporating metal particles of suitable characteristics within them. In this paper the present state of understanding of all these properties is reviewed.     

超重力场下球形炸药水下爆炸实验及数值模拟

常重力条件下,Mach数和Froude数无法同时满足相似。采用离心模型实验,研究水下爆炸冲击波特性及气泡脉动规律,并采用数值模拟方法重现了超重力场下的水下爆炸过程。实验及数值模拟的结果表明,重力的改变基本不影响冲击波的峰值,COLE理论在超重力环境下仍然适用,而超重力场下,小当量炸药可以模拟气泡的脉动迁移过程,其结果可以用于预测大当量炸药深水爆炸的特性。此外,为减少计算时间并提高计算精度,采用将二维冲击波作为初始条件映射到三维模型的建模方法。对于冲击波计算,网格尺寸宜取药包半径的1/20¹/10;对于气泡脉动,宜取药包半径的1/21/10;对于气泡脉动,宜取药包半径的1/2¹。     

Bubble-based acoustic radiation force elasticity imaging

Acoustic radiation force is applied to bubbles generated by laser-induced optical breakdown (LIOB) to study viscoelastic properties of the surrounding medium. In this investigation, femtosecond laser pulses are focused in the volume of gelatin phantoms of different concentrations to form bubbles. A two-element confocal ultrasonic transducer generates acoustic radiation force on individual bubbles while monitoring their displacement within a viscoelastic medium. Tone burst pushes of varying duration have been applied by the outer element at 1.5 MHz. The inner element receives pulse-echo recordings at 7.44 MHz before, during, and after the excitation bursts, and crosscorrelation processing is performed offline to monitor bubble position. Maximum bubble displacements are inversely related to the Young's moduli for different gel phantoms, with a maximum bubble displacement of over 200 microm in a gel phantom with a Young's modulus of 1.7 kPa. Bubble displacements scale with the applied acoustic radiation force and displacements can be normalized to correct for differences in bubble size. Exponential time constants for bubble displacement curves are independent of bubble radius and follow a decreasing trend with the Young's modulus of the surrounding medium. These results demonstrate the potential for bubble-based acoustic radiation force methods to measure tissue viscoelastic properties.     

Experiments to Study the Effect of Light on Electron Bubbles in Liquid Helium

We give a survey of recent experimental and theoretical work on the effect of light on electron bubbles in liquid helium. The light-induced change in the bubbles is measured using an ugtrasonic technique. In helium at temperatures above about 1.7 K, we are able to produce and detect electron bubbles in the 1P quantum state. The properties of the electron bubbles are in agreement with theoretical expectations. However, the application of light to bubbles at low temperatures (T>1.5 K) resugts in. changes in the properties of the bubbles that are not yet understood.     

Mechanism of the Interfacial Reaction of AI_2O_3/Medium Mn Steel Containing Nb

The mechanism of the interfacial reaction of Al_2O_3/medium Mn steel containing Nb was studied bymeans of the observation on the interfacial reaction phenomenon of Al_2O_3/medium Mn steel,andthe analyses on the interracial phases.The results show that when T≥1550℃,the interfacial reac-tion of Al_2O_3/medium Mn steel containing Nb happened.In the medium Mn steel matrix,Nb existsin the form of NbC.NbC are the nucleating base of CO gas bubbles.     

On the existence of stationary solitary waves in a dissipative bubbly liquid

The formation of a solitary wave during the propagation of acoustic perturbations in a liquid containing heat-conducting gas bubbles is revealed for the first time by means of numerical modeling. A physical mechanism explaining the existence of a nondecaying solitary wave in this dissipative medium is proposed, which is based on the reverse influence of the bubble motion dynamics on the heat balance between gas and liquid. This phenomenon is called the moving boundary effect.     

Simulation of the properties of a binary carbon dioxide-water mixture under sub- and supercritical conditions

A method for determining the multiphase thermodynamic equilibriums of a binary mixture expressed in pressure-enthalpy-mixture composition variables is suggested. The use of such variables, in contrast to the classical thermodynamic pressure-temperature-composition variables, makes it possible to determine not only the two-phase, but also three-phase states of a mixture. The method can be used to describe real properties of mixtures in a wide range of pressure and temperature values containing critical points; it can be helpful in modeling of the mixture flows in a porous medium. The suggested problem of calculating the multiphase equilibrium can be visually interpreted in terms of geometry by constructing a convex envelope for the thermodynamic potential of the mixture. This method is used to study the phase diagram of the carbon dioxide-water mixture.     

New phenomena in barbotage and sedimentation in magnetic fluids

New multivelocity model was deduced for a dispersive magnetizable medium: magnetic fluid - gas bubbles or solid particles. Resulting equations may be used for discribing the processes of concentration, separation and barbotage. The characteristics of deduced set were examined. The problem was solved concerning floatation and sedimentation of particles or babbles in a magnetic fluid in a solenoidal magnetic field.     

Development of an Apparatus for the Determination of Spectral Reflectivity at High Temperatures in the Visible

The paper presents a reflectometer for high temperature measurements. In this apparatus, the directional-hemispherical spectral reflectivity is measured by comparing the optical response of the sample to white light with the response of a reference material. The reflected light, collected by an integrating sphere, is dispersed in a spectrograph and detected by an ICCD camera. This procedure allows the simultaneous measurement of the reflectivity in a large, continuous wavelength range (presently 510 to 860 nm). An electrical resistance heater is used to heat the samples up to about 1200 K; for higher temperatures a flash-lamp pumped dye laser is used. To avoid laser induced plasma generation, the integrating sphere is placed inside a vacuum chamber, which also allows measurements under a controlled atmosphere. The response of the apparatus is calibrated to an absolute scale which allows the determination of the sample temperature by fitting the thermal emission spectrum with Planck's formula. To check the performance of the apparatus, measurements on Fe₂O₃ (hematite) and NiO have been carried out.