Clearing effects and radiative transfer in a medium with large-scale fluctuations in the density of scatterers

Radiophysics and Quantum Electronics -     

Kinetics of the thermal decomposition reaction of diethylketone cyclic triperoxide in acetone–toluene and acetone–1‐propanol binary solvent mixtures

The thermal decomposition reaction of diethylketone triperoxide (DEKT) ca. 0.02 M was studied in binary mixtures of acetone–toluene and acetone–1‐propanol at 150 °C. Products of DEKT thermolysis in solution, detected by GC analysis, were diethylketone, bibenzyl and butane. The reactions were explored by GC at different solvent compositions and in each case the reactions followed a pseudo first order kinetic law, up to at least 90% peroxide conversion. The rate coefficient value of the reaction is affected by the solvent properties, showing an increase in the k_obs values with increases in the polarity of the solvent mixture in acetone–toluene systems. Changes in the rate coefficient values are probably caused by the presence of the apolar toluene solvent, which dominates the preferential solvation around the DEKT molecule through non‐specific interactions. In acetone–1‐propanol mixtures the solvation effect is slightly dominated by the specific interactions between the 1‐propanol and a polar intermediate specie represented by the biradical, initially formed. The rate coefficient value increases ca. 6% in the mixture with 0.1 mole fraction of 1‐propanol in comparison with the value in pure acetone; but no more changes in rate coefficient values are observed when the amount of the alcohol increases. The critical state of the reaction (intermediate biradical) is preferentially solvated by the 1‐propanol instead of acetone, but in mixtures of different composition, it is not possible to detect any effect on the reactivity for homolytic rupture of the O? O bond. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of dissolved gases on sonochemical oxidation in a 20 kHz probe system: Continuous monitoring of dissolved oxygen concentration and sonochemical oxidation activity

Dissolved gases have a substantial influence on acoustic cavitation and sonochemical oxidation reactions. Little research on the changes in dissolved gases and the resultant changes in sonochemical oxidation has been reported, and most studies have focused only on the initial dissolved gas conditions. In this study, the dissolved oxygen (DO) concentration was measured continuously during ultrasonic irradiation using an optical sensor in different gas modes (saturation/open, saturation/closed, and sparging/closed modes). Simultaneously, the resulting changes in sonochemical oxidation were quantified using KI dosimetry. In the saturation/open mode using five gas conditions of Ar and O₂, the DO concentration decreased rapidly when O₂ was present because of active gas exchange with the atmosphere, and the DO concentration increased when 100% Ar was used. As a result, the order of the zero-order reaction constant for the first 10 min (k_0-10) decreased in the order Ar:O₂ (75:25) > 100% Ar ≈ Ar:O₂ (50:50) > Ar:O₂ (25:75) > 100% O₂, whereas that during the last 10 min (k_20-30) when the DO concentration was relatively stable, decreased in the order 100% Ar > Ar:O₂ (75:25) > Ar:O₂ (50:50) ≈ Ar:O₂ (20:75) > 100% O₂. In the saturation/closed mode, the DO concentration decreased to approximately 70–80% of the initial level because of ultrasonic degassing, and there was no influence of gases other than Ar and O₂. Consequently, k_0-10 and k_20-30 decreased in the order Ar:O₂ (75:25) > Ar:O₂ (50:50) > Ar:O₂ (25:75) > 100% Ar > 100% O₂. In the sparging/closed mode, the DO concentration was maintained at approximately 90% of the initial level because of the more active gas adsorption induced by gas sparging, and the values of k_0-10 and k_20-30 were almost the same as those in the saturation/closed mode. In the saturation/open and sparging/closed modes, the Ar:O₂ (75:25) condition was most favorable for enhancing sonochemical oxidation. However, a comparison of k_0-10 and k_20-30 indicated that there would be an optimal dissolved gas condition that was different from the initial gas condition. In addition, the mass-transfer and ultrasonic-degassing coefficients were calculated using changes in the DO concentration in the three modes.     

Characterization of heterogeneous interaction in binary mixtures of ethylene glycol oligomer with water, ethyl alcohol and dioxane by dielectric analysis

The associating behaviour of the binary mixtures of ethylene glycol oligomer (EGO), i.e. ethylene glycol (EG), diethylene glycol (DEG) and poly(ethylene glycol)s (PEG200, PEG300, PEG400 and PEG600) with water (W), ethyl alcohol (EA) and 1,4-dioxane (DX) over the entire concentration range at 25 °C have been investigated through their accurately measured values of dielectric constant. The static dielectric constant ε_o, high frequency limiting dielectric constant ε_∞, dielectric relaxation strength Δε, excess dielectric parameters ε^E₀ and ε^E_∞, effective Kirkwood correlation factor g^eff and corrective correlation factor g_f of EGO–W, EGO–EA and EGO–DX mixtures were determined to obtain qualitative and quantitative information about the complex formation through H-bond in these systems. Most of the evaluated dielectric parameters of EG and DEG in different ‘cosolvents’ have different characteristics as compared to the PEG–cosolvent mixture. The observed linear and non-linear behaviour of Δε against EGO monomer unit mole fraction X confirms the variation in the homogeneous structures in their binary mixtures with concentration variation. Appearance of the maximum in ε^E₀ against X plots indicates that a complex stable adduct is formed in the EGO–W mixtures at stoichiometric ratio 1:1.7 for lower oligomers but this ratio seems to be 1.7:1 for higher EGO molecules, which confirms that the EGO size and chain flexibility affects the complex formation between EGO and W. In case of EG–EA mixture 1:1 stoichiometric ratio form stable adduct whereas for higher EGO–EA, it is 3:1, at EGO monomer unit level. The complex formation behaviour of DEG–EA has entirely different characteristics when compared to the other studied EGO–EA mixtures. Although, 1,4-dioxane has weak polar behaviour dielectric properties of EG–DX and DEG–DX confirm the formation of stable adducts at the stoichiometric ratio 2:1 of EGO monomer unit mole fraction to the DX. For the higher EGO–DX mixtures, stable adduct forms at the stoichiometric ratio 9:1. Except DEG–EA mixtures, the EGO–W and EGO–EA form the complex with reduction in the effective number of dipoles. In EG–DX mixtures, the heterogeneous species form with a large reduction in the effective number of dipoles, which changes as the effective number of dipoles increases with the increase in monomer repeat units of EGO. Further the net electronic polarization in these binary mixtures increases due to heterogeneous interaction over the entire mixing concentration range.     

Thermal diffusion in binary mixtures containing molecular gases II: mixtures of N2 with He,Ne, Ar,and Kr and of CO2 with He and Ar

Expressions developed for the thermal diffusion factor, αT, for binary mixtures containing molecular species have been tested for six different atom-molecule interactions. Specifically, the interactions between N₂ and He, Ne, Ar and Kr, plus the interactions between CO₂ and He, Ar, have been examined, in each case using at least two competing modern potential energy surfaces. Detailed expressions in both the ‘total-energy-flux’ and the ‘two-flux’ representations have been developed, and the importance of the anisotropic components of the intermolecular potential energy surfaces in determining the thermal diffusion factor for such mixtures has been determined.     

Electrical conductances of sodium bromide and sodium tetraphenylborate in 2-ethoxyethanol + water mixtures at 308.15, 313.15, 318.15 and 323.15 K

The electrical conductances of the solutions of sodium bromide (NaBr) and sodium tetraphenylborate (NaBPh₄) in 2-ethoxyethanol + water mixed solvent media containing 0.25, 0.50 and 0.75 mass fractions of 2-ethoxyethanol (w₁) have been reported at 308.15, 313.15, 318.15, and 323.15 K. The conductance data have been analyzed by the 1978 Fuoss conductance–concentration equation in terms of the limiting molar conductance (Λ⁰), the association constant (K_A) and the association diameter (R). Of the two electrolytes investigated here, sodium bromide exists essentially in the form of free ions in aqueous 2-ethoxyethanol solutions over the entire temperature range investigated. However, slight ionic association was observed for sodium tetraphenylborate—the extent of which increases with increasing amount of 2-ethoxyethanol in the present mixed solvent media. The solvations of the bromide ion and of the sodium ion were found to be gradually weakened as the 2-ethoxyethanol content of the medium increases. Furthermore, the limiting molar conductivity values of the two electrolytes increase as the temperature increases in all 2-ethoxyethanol + water mixtures which have been described by polynomial equations.     

Conductance studies of NaCl, KCl, NaBr, NaI, NaBPh4, Bu4NI and NaClO4 in water + 2-methoxyethanol mixtures at 298.15 K

The electrical conductances of the solutions of sodium chloride (NaCl), potassium chloride (KCl), sodium bromide (NaBr), sodium iodide (NaI), sodium tetraphenylborate (NaBPh₄), tetrabutylammonium iodide (Bu₄NI) and sodium perchlorate (NaClO₄) in water (1) + 2-methoxyethanol (2) mixtures containing 0.01, 0.025, 0.05, 0.075, 0.10, 0.15 and 0.20 mol fractions of 2-methoxyethanol have been reported at 298.15 K. The conductance data have been analyzed by the Fuoss–Justice equation. The individual limiting ionic conductivities of Na⁺, K⁺, Bu₄N⁺, BPh₄⁻, I⁻, Cl⁻, and Br⁻ ions have been determined using the Fuoss–Hirsch assumption. The dependencies of the limiting molar conductances, Λ_o, and Walden products, Λ_oη, versus mixed solvent composition have been discussed.     

Physalis method for heterogeneous mixtures of dielectrics and conductors: Accurately simulating one million particles using a PC

Prosperetti’s seminal Physalis method, an Immersed Boundary/spectral method, had been used extensively to investigate fluid flows with suspended solid particles. Its underlying idea of creating a cage and using a spectral general analytical solution around a discontinuity in a surrounding field as a computational mechanism to enable the accommodation of physical and geometric discontinuities is a general concept, and can be applied to other problems of importance to physics, mechanics, and chemistry. In this paper we provide a foundation for the application of this approach to the determination of the distribution of electric charge in heterogeneous mixtures of dielectrics and conductors. The proposed Physalis method is remarkably accurate and efficient. In the method, a spectral analytical solution is used to tackle the discontinuity and thus the discontinuous boundary conditions at the interface of two media are satisfied exactly. Owing to the hybrid finite difference and spectral schemes, the method is spectrally accurate if the modes are not sufficiently resolved, while higher than second-order accurate if the modes are sufficiently resolved, for the solved potential field. Because of the features of the analytical solutions, the derivative quantities of importance, such as electric field, charge distribution, and force, have the same order of accuracy as the solved potential field during postprocessing. This is an important advantage of the Physalis method over other numerical methods involving interpolation, differentiation, and integration during postprocessing, which may significantly degrade the accuracy of the derivative quantities of importance. The analytical solutions enable the user to use relatively few mesh points to accurately represent the regions of discontinuity. In addition, the spectral convergence and a linear relationship between the cost of computer memory/computation and particle numbers results in a very efficient method. In the present paper, the accuracy of the method is numerically investigated by example computations using one dielectric particle, one isolated conductor particle, one conductor particle connected to an external source with imposed voltage, and two conductor/dielectric particles with strong interactions. The efficiency of the method is demonstrated with one million particles, which suggests that the method can be used for many important engineering applications of broad interest.     

Enskog’s kinetic theory of dense gases for chemically reacting binary mixtures, II: Light scattering and sound propagation

Enskog’s kinetic theory for a symmetric moderately dense reaction A+A?B+B is used to determine Fick’s and Fourier’s law. The transport coefficients of diffusion, thermal-diffusion rate and thermal conductivity are represented graphically for endothermic and exothermic reactions and are analyzed as a function of the activation energy and of the density of the mixture. The Onsager reciprocity relations are numerically investigated and verified. The problems related to sound propagation and light scattering are investigated for such a mixture and it is shown that the influence of chemical reactions on phase velocity, attenuation coefficient and light scattering spectra is more pronounced for rarefied gases although there is a considerable change in these quantities as the mixture becomes denser.     

Quantification of sonochemical and sonophysical effects in a 20 kHz probe-type sonoreactor: Enhancing sonophysical effects in heterogeneous systems with milli-sized particles

Even though acoustic cavitation has been widely investigated, only few researchers focused on the relationship between sonochemical and sonophysical activities and on the enhancement of sonophysical activity. In this study, sonochemical and sonophysical activities were investigated in a heterogeneous system to understand the relationship between these two activities and to suggest optimal conditions for ultrasonic desorption/extraction processes comprising milli-sized glass beads. The sonochemical activity was quantitatively analyzed using potassium iodide dosimetry in homogeneous and heterogeneous systems. Sonophysical activity was quantitatively and qualitatively analyzed using paint-coated bead desorption tests and aluminum foil erosion tests under three probe positions of “T” (1 cm below the liquid surface), “B” (1 cm above the vessel bottom), and “M” (midpoint between “T” and “B”). Three different sizes of glass beads (diameter: 0.2, 1.0, and 4.0 mm) were used in this study. The highest sonochemical activity was obtained at “B” in both homogeneous and heterogeneous systems. However, three times lower sonochemical activity was observed in the heterogeneous system than in the homogeneous system because significant attenuation and unstable reflection of ultrasound occurred in the bead layer and suspension. Higher sonophysical activity was observed, when the bead size decreased and the probe approached the bottom. However, no significant sonophysical activity was detected when the beads were attached to the bottom. Therefore, the sonophysically active region was the zone around the probe body, opposite to the ultrasound irradiation tip, and only suspended beads could undergo severe cavitational actions. This was confirmed via aluminum foil tests. Several erosion marks on the foil were observed in the area around the probe body, whereas no severe damage was observed at the bottom. Moreover, the degree of sonophysical activity did not change for various saturating gases. This might be due to the different thresholds of sonochemical and sonophysical activities.     

电磁直线加速动态黑洞时空中Dirac粒子的Hawking辐射

研究了作直线加速运动的电磁黑洞视界面上Dirac粒子的Hawking 辐射.首先，构造对称化零 标架，计算旋系数，导出Dirac方程，并对其进行化简.然后，通过引入广义乌龟坐标，在视 界面上将Dirac方程退耦.利用Damour-Ruffini方法，求出了温度以及热谱公式，并对所得结 果进行了讨论. 关键词： 加速动态黑洞 Dirac粒子 Dirac方程 Hawking辐射     

FT‐Raman,FTIR and density functional theory studies of a hydrogen‐bonded formamide:pyridine complex

Raman and IR experiments have been carried out on formamide (FA) and pyridine (Py) mixtures at different compositions. The appearance of a new Raman band at 996 cm⁻¹ (ν₁ region of Py), whose intensity depends on the FA concentration, is assigned to an FA:Py adduct and this result is in excellent agreement with those of other authors who employed noisy light‐based coherent Raman scattering spectroscopy (I⁽²⁾ CARS). Another band at 1587 cm⁻¹ (ν₈ region of Py) has been observed for the first time by using Raman and IR spectroscopies. Its intensity shows the same dependence on the FA concentration and this fact allows us to also attribute it to an FA:Py adduct. The good relationship between the Raman and IR data demonstrates the potential of the vibrational spectroscopy for this kind of study. Owing to higher absolute Raman scattering cross section, the ν₁ region of Py has been chosen for the quantitative analysis and a stoichiometry of 1:1 FA:Py is reported. The experimental data are very well supported by the density functional theory (DFT) calculation, which was employed for the first time to the present system. Furthermore, the actual investigation shows an excellent agreement with those reported from computational calculations for similar systems. A comparison with our previous studies confirms that the solvent dielectric constant determines the stoichiometry of a given Lewis acid–base adduct in the infinite dilution limit. Copyright © 2009 John Wiley & Sons, Ltd.     

THz radiation generation via the interaction of two‐colour ultra‐short laser pulses with SO2 and NH3 gases

In this work, using a two‐dimensional particle‐in‐cell Monte Carlo collision computation method, terahertz (THz) radiation generation via the interaction of two‐colour, ultra‐short, high‐power laser pulses with the polyatomic molecular gases sulphur dioxide (SO₂) and ammonia (NH₃) is examined. The influence of SO₂ and NH₃ pressures and two‐colour laser pulse parameters, i.e., pulse shape, pulse duration, and beam waist, on the THz radiation generation is studied. It is shown that the THz signal generation from SO₂ and NH₃ increases with the background gas pressure. It is seen that the THz emission intensity for both gases at higher laser pulse durations is higher. Moreover, for these polyatomic gases, the plasma current density increases with increase in the laser pulse beam waist. A more powerful THz radiation intensity with a larger time to peak of the plasma current density is observed for SO₂ compared to NH₃. In addition, many THz signals with small intensities are observed for both polyatomic gases. It is seen that for both SO₂ and NH₃ the generated THz spectral intensity is higher at higher gas pressures.     

高能粒子辐照二氧化硅玻璃E′色心形成机理研究

考虑高能粒子辐照二氧化硅玻璃形成E′色心的情况,建立了E′色心形成的动力学模型,得到了E′色心浓度与辐照剂量的关系式. 结果表明,在高能粒子辐照情况下,E′色心的形成包括两个过程,即色心的创造过程和色心的激活过程. 色心的创造过程主要由二氧化硅网格中疲劳键的断裂形成或网格中氧移位形成,E′色心浓度随剂量的变化呈线性增长.色心的激活过程主要由二氧化硅玻璃中固有点缺陷形成,E′色心浓度随剂量的变化呈饱和趋势.理论结果和实验结果符合很好,说明建立的模型是有效的. 关键词： 二氧化硅玻璃 E′色心 辐照剂量 动力学模型     

A method for determining optical constants, dimensions, and concentrations of “soft” absorbing particles in the brightening band region

We investigate the possibilities of creating a method for estimating the optical constants, dimensions, and concentrations of “soft” absorbing particles by applying a theoretical analysis of the angular dependence of the intergrated indicatrix, overall characteristics of light scattering, and absorption on the phase shift and diffraction parameter of particles in the brightening band region. We show that using the investigated optical characteristics, it is possible to determine the unknown parameters of a suspension from experimental data. Institute of Biophysics, Siberian Branch of the Russian Academy of Sciences, Akademgorodok, Krasnoyarsk, 660036, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 807–812, November–December, 1997.     

Intracavity parametric conversion of radiation from a pulsed Nd:YVO<Subscript>4</Subscript> laser with high-power diode pumping

We have achieved intracavity parametric conversion of the radiation from a laser based on Nd:YVO₄ with high-power diode pumping. An LiF^2- crystal was used as the passive Q-switch for the Nd:YVO₄ laser. We have shown that by using an active element in the master laser with a passive region, we can form pulsed laser beams at a wavelength of 1.57 μm with peak power 3.2 kW and repetition rates up to 80 kHz, with beam quality parameter 1.4–1.8. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 5–8, January–February, 2006.     

The effective ionization coefficients and electron drift velocities in gas mixtures of CF3I with N2 and CO2 obtained from Boltzmann equation analysis

The electron swarm parameters including the density-normalized effective ionization coefficients(α-η)/N and the electron drift velocities V e are calculated for a gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of a steady-state Townsend(SST) experiment.The overall density-reduced electric field strength is from 100 Td to 1000 Td(1 Td = 10-17V·cm2),while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%.From the variation of(αη)/N with the CF3I mixture ratio k,the limiting field strength(E/N) lim for each CF3I concentration is derived.It is found that for the mixtures with 70% CF3I,the values of(E/N) lim are essentially the same as that for pure SF 6.Additionally,the global warming potential(GWP) and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of application in the gas insulation of power equipment.