Determination of radon partitioning between groundwater and atmosphere by liquid scintillation counter

A simple method for the determination of the air?Cwater partition coefficient (K_air/water) of radon (Rn-222) was studied using a liquid scintillation counter. In the present work, the radon activity of groundwater phase in a closed container was measured and used to calculate the partition coefficient instead of the radon activity of gaseous phase in other works. The partition coefficient was determined for four groundwater samples by using a modified equilibrium partition coefficient in closed system method. The effect of temperature on the partition coefficient was investigated at 0, 10, 20 and 30?°C. Within the temperature range, the partition coefficients were 1.72?C2.03, 2.11?C2.28, 2.78?C3.92 and 4.93?C5.61 at 0, 10, 20, and 30?°C, respectively. It was found that the effect of temperature on the air?Cwater partition coefficient of groundwater radon was agreed well with literature values.     

An experimental and theoretical study on the kinetics of the reaction between 4‐hydroxy‐3‐hexanone CH3CH2C(O)CH(OH)CH2CH3 and OH radicals

Experimental and theoretical rate coefficients are determined for the first time for the reaction of 4‐hydroxy‐3‐hexanone (CH₃CH₂C(O)CH(OH)CH₂CH₃) with OH radicals as a function of temperature. Experimental studies were carried out using two techniques. Absolute rate coefficients were measured using a cryogenically cooled cell coupled to the pulsed laser photolysis‐laser‐induced fluorescence technique with temperature and pressure ranges of 280‐365 K and 5‐80 Torr, respectively. Relative values of the studied reaction were measured under atmospheric pressure in the range of 298‐354 K by using a simulation chamber coupled to a FT‐IR spectrometer. In addition, the reaction of 4H3H with OH radicals was studied theoretically by using the density functional theory method over the range of 278‐350 K. Results show that H‐atom abstraction occurs more favorably from the C–H bound adjacent to the hydroxyl group with small barrier height. Theoretical rate coefficients are in good agreement with the experimental data. A slight negative temperature dependence was observed in both theoretical and experimental works. Overall, the results are deliberated in terms of structure–reactivity relationship and atmospheric implications.     

Effective Permittivity of a Multi-Phase System: Nanoparticle-Doped Polymer-Dispersed Liquid Crystal Films

This paper studies the effective dielectric properties of heterogeneous materials of the type particle inclusions in a host medium, using the Maxwell Garnet and the Bruggeman theory. The results of the theories are applied at polymer-dispersed liquid crystal (PDLC) films, nanoparticles (NP)-doped LCs, and developed for NP-doped PDLC films. The effective permittivity of the composite was simulated at sufficiently high frequency, where the permittivity is constant, obtaining results on its dependency on the constituents’ permittivity and concentrations. The two models are compared and discussed. The method used for simulating the doped PDLC retains its general character and can be applied for other similar multiphase composites. The methods can be used to calculate the effective permittivity of a LC composite, or, in the case of a composite in which one of the phases has an unknown permittivity, to extract it from the measured composite permittivity. The obtained data are necessary in the design of the electrical circuits.     

Preparation and Some Properties of Lithium Vanadium Bronzes

Lithium vanadium bronzes with composition formula Li_xV₂O₅ (0.04 ≤ × ≤ 0.92) have been prepared by solid‐state reaction at 650 °C in argon atmosphere. The obtained products were characterized by X‐ray powder diffraction and IR spectroscopy. The results reveal that four phases are present in the range from x = 0.04 to 0.92, namely α, β, β′, and γ phase. The magnetic susceptibility for the investigated bronzes was measured using the conventional Gouy's method. The values of the effective magnetic moments, as calculated from experimental data, indicate the presence of V⁴⁺ ions in all bronze samples. The electrical conductivity as a function of temperature and lithium content was measured in the temperature range from room temperature to 483 K. The electrical conductivity of the bronzes is found to be affected by lithium content. The values of the electrical conductivity increase with temperature for the prepared samples and both electronic and ionic conduction are discussed.     

A mild method for the synthesis of bis-pyrazolo[3,4-b:4′,3′-e]pyridine derivatives

A mild and efficient method for the synthesis of bispyrazolo[3,4-b:4′,3′-e]pyridines from 5-aminopyrazoles and aromatic aldehydes using an inexpensive FeCl₃ catalyst is reported. The reaction temperature was reduced from 220–250?°C to 130?°C compared to conventional methods. A large proportion of the products precipitated directly from the mixture at room temperature. Aliphatic and α,β-unsaturated aldehydes selectively resulted in formation of the corresponding 1H-pyrazolo[3,4-b]pyridine derivatives. A possible domino reaction mechanism was also proposed. Several aryl alkynyl groups were introduced to these tricyclic molecules via the Sonogashira coupling reaction.     

Permittivity of a composite of cellulose,mineral oil,and water nanoparticles: theoretical assumptions

The paper presents results of testing permittivity of an oil-impregnated electric pressboard containing water nanoparticles depending on AC frequency, moisture content level and the temperature of samples. A new method has been developed for converting experimentally obtained frequency dependences of permittivity determined with the frequency-domain spectroscopy (FDS) to the reference temperature of 293 K (20 °C) using exponential dependence of the relaxation time versus temperature. Activation energy of the permittivity relaxation time has been determined for a moist oil-impregnated electric insulation pressboard. It has been established that variations of the moisture content level in a composite of cellulose, mineral oil, and water nanoparticles do not cause any changes in the relaxation time activation energy value, neither in energy states of electrons in potential wells nor in the structure of water nanoparticles. It has been also found that the conversion of experimentally obtained permittivity versus frequency dependences determined with the FDS method to the reference temperature of 293 K (20 °C) eliminates temperature dependences that occur in characteristics based directly on measurement results. Once the relative permittivity is converted to the reference temperature it is only its dependence on the moisture content level that remains.     

液-液溶解度法与气-液色谱法研究溶剂-溶剂的相互作用

测量了角鲨烷(B)+邻苯二甲酸二丁酯(C)的溶解度相图, 应用HSFH二元系公式推算得相互作用参数Abc; 用气-液色谱测量了若干正构烷烃、环烷烃用作探测溶质(A)在(B+C)混合溶剂中的无限稀活度系数, 应用HSFH三元系公式推算得相互作用参数Abc, 两者符合热力学一致性。     

Nonstoichiometry and electronic defects in yttrium iron garnet

Results are presented of a thermogravimetrical analysis of yttrium iron garnet, Y₃Fe₅O_12?δ, in the temperature range 950–1270°C. From these measurements the oxygen vacancy concentration δ is obtained for partial oxygen pressures between 1 and 10^?5 atm. The data can be fitted with a relation $\text{δ = A}\text{exp}\text{(}\text{?E}\text{kT}\text{)}$. Values of A and E are given for different values of P_O2. The combined data from electrical conductivity measurements, measurements of Seebeck coefficients, and thermogravimetric analysis, are used to calculate the concentrations of point defects in the garnet lattice. The results are expressed in terms of equilibrium reaction constants. The model is also used to analyze diffusivity data.     

Pair correlation functions and the self-diffusion coefficient of Lennard-Jones liquid in the modified free volume theory of diffusion

In this paper, we apply the Matteoli-Mansoori empirical formula for the pair correlation function of simple fluids obeying the Lennard-Jones potential to calculate reduced self-diffusion coefficients on the basis of the modified free volume theory. The self-diffusion coefficient thus computed as functions of temperature and density is compared with the molecular dynamics simulation data and the self-diffusion coefficient obtained by the modified free volume theory implemented with the Monte Carlo simulation method for the pair correlation function. We show that the Matteoli-Mansoori empirical formula yields sufficiently accurate self-diffusion coefficients in the supercritical regime, provided that the minimum free volume activating diffusion is estimated with the classical turning point of binary collision at the mean relative kinetic energy 3k(B)T/2, where k(B) is the Boltzmann constant and T is the temperature. In the subcritical regime, the empirical formula yields qualitatively correct, but lower values for the self-diffusion coefficients compared with computer simulation values and those from the modified free volume theory implemented with the Monte Carlo simulations for the pair correlation function. However, with a slightly modified critical free volume, the results can be made quite acceptable.     

Lindane Adsorption-Desorption on Chitin in Sea Water

Abstract

The adsorption and desorption processes by solid materials are important in determining the movement and fate of pesticide compounds in aquatic systems. Chitin is one of the constituents of natural organic matter and may serve as a model organic phase for studying the pesticide adsorption-desorption in marine systems. The lindane adsorption-desorption to chitin has been studied as a function of chitin concentration (2.5 gl^?1 to 12.5 gl^?1), temperature (5 to 45°C), pH (1.5 to 8) and salinity (15‰ to 36‰). Both, Freundlich and linear isotherms for the adsorption and desorption processes were used to represent the experimental data. Two-site Langmuir isotherm can describe well the measured sorption isotherm. The adsorbent-concentration effect and the adsorption-desorption hysteresis show the existence of different classes of site with different accessibility. Thus, the adsorption-desorption reaction of lindane is the result of more than a single mechanism. An increase in temperature (ΔH = ?4.0 ± 0.7 Kcal mol^?1) and a decrease in salinity resulted in both lower lindane adsorption and in a more reversible process. An increase of pH resulted in lower adsorption partition coefficients.     

Modification of the GV-MSA model in obtaining the activity and osmotic coefficients of aqueous electrolyte solutions

In this work a modified form of the Ghotbi–Vera Mean Spherical Approximation model (MGV-MSA) has been used to correlate the mean ionic activity coefficients (MIAC) for a number of symmetric and asymmetric aqueous electrolyte solutions at 25 °C. In the proposed model the hard sphere as well as the electrostatic contributions to the MIAC and the osmotic coefficient of the previously GV-MSA model has been modified. The results of the proposed model for the MIAC of the electrolyte solutions studied in this work are used to directly calculate the values of the osmotic coefficients without introducing any new adjustable parameter. In the MGV-MSA model the cation diameter as well as the relative permittivity of water depends on the electrolyte concentration. Having considered such dependency for both cation and relative permittivity for water in an electrolyte solution the modification of the GV-MSA has been made. It should be stated that in the MGV-MSA model the anion diameter in the solution similar to that in the GV-MSA model remains constant and independent of the electrolyte concentration. The results obtained from the proposed model have been favorably compared with those of the GV-MSA model. The results showed that the MGV-MSA model can more accurately correlate the MIAC of the single electrolyte solutions than those of the GV-MSA model. The same comparison has been observed in case of the osmotic coefficients for the electrolyte solutions studied in this work. It should be noted that in order to do an unequivocal comparison between the results obtained from the models used in this work the same minimization procedure and the same experimental data for the MIAC and the osmotic coefficients have been used. Also it should be mentioned that in the MGV-MSA model the conversion from the McMillan–Mayer (MM) framework to that of the Lewis–Randall (LR) has been performed. It has been concluded that such transformation can affect the results in particular at higher electrolyte concentrations.     

Applications of automatic differentiation to the time‐dependent Schrödinger equation

A new approach based upon the Taylor series method is proposed for propagating solutions of the time‐dependent Schrödinger equation. Replacing the spatial derivative of the wave function with finite difference formulas, we derive a recursive formula for the evaluation of Taylor coefficients. The automatic differentiation technique is used to recursively calculate the required Taylor coefficients. We also develop an implicit scheme for the recursive evaluation of these coefficients. We then advance the solution in time using a Taylor series expansion. Excellent computational results are obtained when this method is applied to a one‐dimensional reflectionless potential and a two‐dimensional barrier transmission problem. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Vapor-liquid equilibria for the system water + tert.-pentanol at 4 temperatures

Precise isothermal vapor-liquid equilibrium data at 10, 30, 55 and 70°C for the system water + tert.-pentanol were measured using a computer-operated differential static apparatus. Activity coefficients at infinite dilution were derived from the experimental P − x data in the dilute region using a flexible Legendre polynomial, and the vapor-liquid-liquid locus was derived directly from the P − x data near the liquid-liquid phase boundary. Heteroazeotropic points were measured directly by distillation using a rotating band column. Furthermore the UNIQUAC and the NRTL models were used to correlate the experimental P − x data and to derive the azeotropic data.

Experimental H^E data were taken from literature and used together with the experimental P − x data to simultaneously fit temperature dependent interaction parameters for UNIQUAC and NRTL. The parameters were used to predict the azeotropic composition over a large temperature range. The results were compared with those of a simple analytical thermodynamic equation using only the pure component vapor pressure data, heats of mixing in the heterogeneous region and the azeotropic composition at one temperature.

Heats of mixing were measured at 140°C with the help of a flow calorimeter in order to determine the slope of H^E vs. x₁ in the heterogeneous region. The H^E data were used to check the reliability of the G^E model parameters and the equation to calculate the temperature dependence of the heteroazeotropic composition.     

Canonical statistical adiabatic channel model calculations of the H + CH3 → CH4 recombination reaction on an ab initio potential energy surface. The role of the transitional modes

The canonical formalism of the statistical adiabatic channel model is used to calculate limiting high pressure rate constants for the H + CH₃ → CH₄ recombination reaction on a recently reported analytic potential energy surface based on ab initio calculations. An effective adiabatic channel potential which incorporates the G_?? matrix element of the twofold degenerate H₃C? H transitional bending mode, quartic anharmonicity, and state selected mode coupling effects is implemented. The rate constants calculated over the temperature range 200–1000 K are in very good agreement with recent canonical variational transition state theory calculations performed on the same surface. The comparison with experimental results is also discussed.     

Diffusion energies of oxygen diffusing into polystyrene (PS)/poly (N‐isopropylacrylamide) composites

Diffusion coefficient of oxygen penetrating into polystyrene (PS) latex/poly (N‐isopropylacrylamide) (PNIPAM) microgel composite films were measured using Fluorescence technique. Three different (5, 15, and 40 wt%) PS content films were prepared from PS/PNIPAM mixtures. Diffusivity of PS/PNIPAM composite films were studied by diffusion measurements which were performed over the temperature range of 24–70°C. Pyrene was used as the fluorescent probe. The diffusion coefficients (D) of oxygen were determined using the Stern–Volmer fluorescence quenching method combined with Fickian transport and were computed as a function of temperature for each PS content film. The results showed that D values were strongly dependent on both temperature and PS content in the film. Diffusion energies were measured and found to be dependent on the composition of the composite films. Copyright © 2011 John Wiley & Sons, Ltd.     

Rate Coefficients of Roaming Reaction H+MgH Using Ring Polymer Molecular Dynamics

The ring-polymer molecular dynamics (RPMD) was used to calculate the thermal rate coefficients of the multi-channel roaming reaction H+MgH→Mg+H₂. Two reaction channels, tight and roaming, are explicitly considered. This is a pioneering attempt of exerting RPMD method to multi-channel reactions. With the help of a newly developed optimization-interpolation protocol for preparing the initial structures and adaptive protocol for choosing the force constants, we have successfully obtained the thermal rate coefficients. The results are consistent with those from other theoretical methods, such as variational transition state theory and quantum dynamics. Especially, RPMD results exhibit negative temperature dependence, which is similar to the results from variational transition state theory but different from the ones from ground state quantum dynamics calculations.     

Transport properties of alternative fuel microemulsions based on sugar surfactant

Electrical conductivity of fuel microemulsion composed of diesel, pentanol, water, and sucrose laurate as surfactant was investigated over a wide range of water contents varying from 0 to 90?wt% and temperature varying from 10°C to 50°C. Conductivity measurements were performed on samples, the composition of which lie along the one-phase channel using a conductivity meter. Activation energy of conduction flow was evaluated. The hydrodynamic radius as a function of temperature in the aqueous phase-rich region (90?wt%) was measured using the dynamic light scattering (DLS) method. The microstructure of the microemulsion was further investigated by NMR diffusometry by which the self-diffusion coefficients for water were determined at 25°C. Electrical conductivity increases with water content up to 40?wt% and the percolation threshold was observed, and then stabilizes between 40 and 80?wt% then decreases. Percolation threshold temperature at constant composition was monitored as 36°C for water contents below 80?wt% and as 34°C for water contents above that. As predicted by the conductivity measurements, the determined self-diffusion coefficients of water confirmed the structural transition from discrete W/O droplets to bi-continuous phase and finally to O/W droplet microemulsion.     

Studies on ignition and afterburning processes of KClO4/Mg pyrotechnics heated in air

Thermal behavior of KClO₄/Mg pyrotechnic mixtures heated in air was investigated by thermal analysis. Effects of oxygen balance and heating rates on the TG?CDSC curves of mixtures were examined. Results showed that DSC curves of the mixtures had two exothermic processes when heated from room temperature to 700?°C, and TG curve exhibited a slight mass gain followed by a two-stage mass fall and then a significant mass increase. The exothermic peak at lower temperature and higher temperature corresponded to the ignition process and afterburning process, respectively. Under the heating rate of 10?°C?min^?1, the peak temperatures for ignition and afterburning process of stoichiometric KClO₄/Mg (58.8/41.2) was 543 and 615?°C, respectively. When Mg content increased to 50%, the peak ignition temperature decreased to 530?°C, but the second exothermic peak changed little. Reaction kinetics of the two exothermic processes for the stoichiometric mixture was calculated using Kissinger method. Apparent activation energies for ignition and afterburning process were 153.6 and 289.5?kJ?mol^?1, respectively. A five-step reaction pathway was proposed for the ignition process in air, and activation energies for each step were also calculated. These results should provide reference for formula design and safety storage of KClO₄/Mg-containing pyrotechnics.     

Isopiestic Determination of Osmotic and Activity Coefficients for Solutions of LiCl, LiBr, and LiNO3 in 2-Propanol at 25°C

The osmotic coefficients of lithium chloride, lithium bromide, and lithium nitrate in 2-propanol have been measured by the isopiestic method at 25^°C. Sodium iodide was used as the isopiestic standard. The molality ranges covered were from 0.2 to 1.5 for LiCl and LiBr, and to 1.9 mol-kg^-1 for LiNO₃. The system of equations developed by Clegg–Pitzer and Pitzer were used to fit each set of osmotic coefficients. The experimental osmotic coefficient data are successfully correlated with these models. The parameters from the fit were used to calculate the mean molal activity coefficients.     

Quick method for determination of equilibrium temperature of calcium carbonate dissociation

A quick method for determination of equilibrium temperature of high temperature reactions, which is inexpensive and suitable for small industrial laboratories, is reported. Reaction of high temperature dissociation of calcium carbonate is used as example for quick method application. The method is based on calorimetric measurement, Hess Law, and thermodynamic calculations. The calibrated calorimeter is used to determine enthalpy change for reactions CaCO₃(s)?+?HCl(l), Ca(s)?+?2HCl(l), and CaO(s)?+?2HCl(l). By application of Hess??s energy cycle, enthalpies of formation of calcium carbonate and calcium oxide were determined. Acquired results were used to calculate enthalpy change for carbonate dissociation reaction. Calculated enthalpy change value was used for free energy change in dependence of temperature and also for equilibrium constant in dependence of temperature calculation using equations derived from basic thermodynamic equations. Using this method, equilibrium temperature for calcium carbonate dissociation reaction is found to be equal to 1154.14?K, which confirms accuracy of the method.