Mixture Of Impurities Research Articles

Modelling and numerical methods for the dynamics of impurities in a gas

AbstractThe dynamics of a mixture of impurities in a gas can be represented by a system of linear Boltzmann equations for hard spheres. We assume that the background is in thermodynamic equilibrium and that the polluting particles are sufficiently few (in comparison with the background molecules) to admit that there are no collisions among couples of them. In order to derive non‐trivial hydrodynamic models, we close the Euler system around local Maxwellian's which are not equilibrium states.The kinetic model is solved by using a Monte Carlo method, the hydrodynamic one by implicit–explicit Runge–Kutta schemes with weighted essentially non‐oscillatory reconstruction (J. Sci. Comput. 2005; 25(1–2):129–155). Several numerical tests are then computed in order to compare the results obtained with the kinetic and the hydrodynamic models. Copyright © 2007 John Wiley & Sons, Ltd.

Surface tension and capillary waves at the nematic-isotropic interface in ternary mixtures of liquid crystal, colloids, and impurities

In mixtures of thermotropic liquid crystals with spherical poly(methyl methacrylate) particles, self-supporting networklike structures are formed during slow cooling past the isotropic-to-nematic phase transition. Experimental results support the hypothesis that a third component, alkane remnants slowly liberated from the particles, plays a crucial role. A theoretical model, based on the phenomenological Landau-de Gennes, Carnahan-Starling, and hard-sphere crystal theories, is developed to describe the continuous phase separation in a ternary nematic-impurity-colloid mixture. The interfacial tension and the dispersion relation of the surface modes of the nematic-isotropic interface are determined. The colloids decrease the interfacial tension and the damping rate of surface waves, whereas impurities act in an opposite way. This should strongly influence the formation of abovementioned networklike structures and could help explain some of their rheological properties.

(Liquid + Liquid) Equilibria for Water + Ethanol + Citral Multicomponent System at 303.15 K

Liquid−liquid equilibrium data for the system water + ethanol + citral (neral + geranial + impurities) at 303.15 K were obtained, considering that citral is composed by two geometrical isomers along with a complex mixture of impurities. All organic chemicals contained in the commercial citral were quantified by gas chromatography using a flame ionization detector rather than a thermal conductivity detector. Moreover, this last detector was used to quantify water and ethanol. To obtain the equilibrium data for this system, several mixtures that contain different ratios of the compounds, two with different ratios of (water + ethanol), one with the (neral + geranial) ratio corresponding to the commercial citral, and two with different ratios of (citral + ethanol), were studied. The influence of the equilibrium concentrations of ethanol and water on the neral and geranial distribution was also studied. Experimental results show that ethanol enhances the solubility of citral in water.

The Impact of Hydrogen Fuel Contaminates on Long-Term PMFC Performance

We have studied the effects of H2S and fuel impurity mixtures on hydrogen polymer fuel cell performance. The tests included a range of H2S concentrations, exposure times, and multiple impurity mixtures at various operating conditions such as cell voltage and times of exposure. Analytical methods included fuel cell polarization experiments, cyclic voltammetry, and effluent water and gas analysis using specific ion sensor probes. H2S concentrations as low as 10 ppb, produced negative effects on fuel cell performance. The extent of sulfur poisoning of the anodes was also shown to be a strong function of fuel cell operating voltage during H2S exposure.

Plasma disturbance sources in the postsunset low-latitude outer ionosphere according to the Intercosmos-Bulgaria-1300 satellite

The satellite low-latitude and midlatitude measurements of the disturbed postsunset plasma density and electron temperature at altitudes of ∼900 km have been compared with the data of incoherent scattering and high-altitude rocket launching at the corresponding local time. It has been found that plasma density disturbances are independently caused by the turbulent interaction between atmospheric masses of gas and plasma ascending from heated and not yet cooled ionospheric regions and cooling masses descending from protonospheric altitudes. Plasma regions with an energetically nonequilibrium vertical density distribution of the mixture of heavy ion impurity (O+) and major light ions (H+) can simultaneously appear, as a result of which the gradient-drift impurity instability is generated. If this instability is sufficiently developed, there appears an anomalous ion drift with the formation of real plasma regions of decreased density. All these phenomena generate different irregularities in a wide range of scales: from several tens or hundreds of meters to several hundreds of kilometers.

Subsurface ice as a microbial habitat

We determine the physicochemical habitat for microorganisms in subsurface terrestrial ice by quantitatively constraining the partitioning of bacteria and fluorescent beads (1–10 m) between the solid ice crystals and the water-filled veins and boundaries around individual ice crystals. We demonstrate experimentally that the partitioning of spherical particles within subsurface ice depends strongly on size but is largely independent of source particle concentration. Although bacteria are shown consistently to partition to the veins, larger particles, which would include eukaryotic cells, become trapped in the crystals with little potential for continued metabolism. We also calculate the expected concentrations of soluble impurities in the veins for typical bulk concentrations found in natural ice. These calculations and scanning electron microscope observations demonstrate a concentrated chemical environment (3.5 M total ions at 10 C) in the veins, where bacteria were found to reside, with a mixture of impurities that could sustain metabolism. Our calculations show that typical bacterial cells in glacial ice would fit within the narrow veins, which are a few micrometers across. These calculations are confirmed by microscopic images of spherical, 1.9-m-diameter, fluorescent beads and stained bacteria in subsurface veins. Typical bacterial concentrations in clean ice (102–103 cells/mL) would result in concentrations of 106–108 cells/mL of vein fluid, but occupy only a small fraction of the total available vein volume (0.2%). Hence, bacterial populations are not limited by vein volume, with the bulk of the vein being unoccupied and available to supply energy sources and nutrients.

Transformation to L10 structure in FePd nanoparticles synthesized by modified polyol process

FePd nanoparticles were prepared by the modified polyol process, i.e. simultaneous reduction of palladium acetylacetonate and thermal decomposition of iron pentacarbonyl in a solvent. The well-dispersed FePd particles, with the average particle size of ~8.4 nm, were obtained using diphenyl ether as a solvent. The structure of FePd nanoparticles transformed to L10 structure from face centered cubic (fcc) structure after annealing at 600 °C for 1 h in vacuum. The coercivity of the ordered FePd nanoparticles increased to ~2 kOe at 5 K from ~0.6 kOe in the fcc as-made FePd nanoparticle. On the other hand, FePd nanoparticles, synthesized based on the conventional modified polyol process using dioctyl ether as a solvent, showed no structural transformation after annealing up to 700 °C. This is explained in terms of the interruption of thermal diffusion of Fe and Pd atoms during the thermal treatment due to the mixture of interstitial carbon impurity in the synthesis process using dioctyl ether as a solvent.

Quantitative and Isomeric Determination of Amphetamine and Methamphetamine from Urine using a Nonprotic Elution Solvent and R(-)- -Methoxy- -Trifluoromethylphenylacetic Acid Chloride Derivatization

Forensic Urine Drug Testing Laboratories often requires two confirmatory methods for a methamphetamine positive screen. First, methamphetamine is identified and quantitated using gas chromatography-mass spectrometry. If the total methamphetamine concentration is above the administrative cutoff level, the isomeric composition must be determined. This eliminates a possible contribution by over-the-counter cold medications that contain l-methamphetamine (Vick's inhalers). Products that contain only the l-isomer of methamphetamine must be distinguishable from prescription or illicitly manufactured methamphetamine, which consists mainly of the d-isomer. Optically impure derivatizing reagents will produce an impure mixture from a pure isomeric compound. Therefore, methods utilizing impure reagents can prove problematic when interpreting results. Use of an optically pure chiral derivatizing reagent, such as R(-)-alpha-methoxy-alpha-trifluoromethylphenylacetic acid chloride, allows for the creation and measurement of chromatographically separable isomeric compounds. The novel method described here utilizes a polymer-based solid-phase column adapted to a positive pressure manifold extraction system and a one-step derivatization process that occurs directly in the elution solvent. This methodology eliminates an elution solvent dry-down step that may adversely affect recovery of volatile amphetamine compounds. Although the method was designed for the quantitative analysis of the isomers of amphetamine and methamphetamine, it can be adapted for use with a wide range of phenethylamines including methylenedioxyamphetamine, N-methylenedioxymethamphetamine, and possibly N-methylenedioxyethylamphetamine. The linear range for quantitation was 25-10,000 ng/mL for d,l-methamphetamine and d,l-amphetamine, and correlation coefficients were 0.997 or better. The coefficient of variation for all four analytes did not exceed 2.8%. Concentrations analyzed ranged from 500 to 4000 ng/mL (n=40). The method allows for a simple and accurate quantitation and isomeric determination of amphetamine and methamphetamine using a process that eliminates extraction and derivatization complications common in current methods.

Purification and characterisation of poly(2-methoxyaniline-5-sulfonicacid acid)

The chemical oxidative synthesis of water soluble sulfonated polyaniline, poly (2-methoxy aniline-5-sulfonic acid) (PMAS) has been shown to result in an impure mixture of polymeric isomers. A tangential cross flow dialysis system has been developed to rapidly and efficiently separate high molecular weight polymer from low molecular weight oligomers, and results compared to conventional tubing dialysis. Characterisation of the purified polymer fractions has been made using UV-vis spectroscopy, gel permeation chromatography, cyclic voltammetry, conductivity measurement and thermal analysis. Results indicate that while the conventional dialysis tubing is not able to separate the mixture of high and low molecular weight materials efficiently, the cross flow dialysis is able to separate them more rapidly and efficiently. Purified high molecular weight PMAS exhibited enhanced electrical conductivity and significant property changes with respect to tubing dialysed PMAS. The pure PMAS, which is the high molecular weight species (Mw 10157 Da) obtained from the cross flow dialysis, has a twofold higher conductivity than the impure PMAS dialysed by the conventional method.

Prediction of radiative transfer in an aluminium-recycling furnace

AbstractThe radiation transport in an industrial, oxygen-enriched, natural-gas-fired furnace has been modelled. In such furnaces, the presence of oxidizing species adjacent to the molten aluminium forms a layer of dross (a porous mixture of aluminium oxide, soot, and impurities from the recycled aluminium) on the surface. The impact of the dross formation on the thermal transport from the combustion products to the molten aluminium is studied. The furnace radiation transport is assumed to be one-dimensional, and the coupling of radiation with conduction through the dross layer is approximated. Measurements of primary radiating species concentrations were taken from previously published measurements, and the temperatures were estimated from the firing stoichiometry. The radiation transfer was modelled using the Spectral Line Weighted-sum-of-grey-gases method previously published for multicomponent, non-homogeneous, non-isothermal gas mixtures with soot. Although the dross layer presents a more absorbing la...

Microstructures of YBa/sub 2/Cu/sub 3/O/sub 7-X/ films prepared by low-pressure oxygen atmosphere post-annealing of precursor films using Y, BaF/sub 2/ and Cu

Transmission electron microscopy (TEM), reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) are used to characterize the microstructure and surface topography of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films. The YBCO films of approximately 0.2 and 0.8 /spl mu/m thickness are prepared by a post-annealing of precursor films of co-evaporated Y, BaF/sub 2/ and Cu. The annealing conditions are the same for all cases except for the temperature elevation rate. RHEED patterns corresponding to the YBCO structure are observed in both the samples after annealing at 700 /spl deg/C for 30 minutes. The XRD patterns show that both YBCO films have primarily c-axis orientation. According to TEM observation results, the YBCO film of 0.2 /spl mu/m thickness is epitaxially grown from a substrate surface. In the case of thicker films of 0.8 /spl mu/m, the bottom region of the film is epitaxial YBCO, while the top region is a mixture of a-axis orientation, other orientations and impurities.

Hydrogen atoms in impurity-helium solids.

Electron spin resonance (ESR) is employed to study atomic impurities (H and D) stabilized in impurity-helium (Im-He) solids at 1.35-1.5 K. The kinetics of the low temperature tunneling exchange reactions (D+H2-->H+HD, D+HD-->H+D2) are investigated in Im-He samples containing several different mixtures of hydrogen and deuterium impurities. The ESR line structures help determine the local environment of atoms trapped in Im-He solids. High concentrations of atomic hydrogen stored in Im-He solids may ultimately find applications in energy storage, matrix-isolation spectroscopy, and studies of different quantum statistical effects.

STEADY STATE SIMULATION OF PHOSPHORIC ACID CONCENTRATION PROCESS

Steady-state simulation of wet phosphoric acid concentration process was carried out using process engineering simulator SCAPE (Software for Computer Aided Process Engineering), with the aim to study process performances. Industrial phosphoric acid was characterized by a mixture of phosphoric acid, water, and impurities in aqueous solution. The major phosphoric acid impurities were represented by a pseudocomponent. The Peng–Robinson equation of state was adapted to calculate phase equilibrium for industrial phosphoric acid using the pseudocomponent approach. The simulation of many points of cycle of phosphoric acid concentration process was carried out. The results obtained were compared to process data. The mean absolute relative error was within 0.4% for boiler temperature, 0.9% for heat exchanger outlet temperature, 0.3% for P2O5 mass content of concentrated phosphoric acid, and 0.4% for concentrated phosphoric acid mass flow rate. The sensitivity of P2O5 mass concentration of concentrated phosphoric acid vs. the main process parameters such as steam and weak phosphoric acid feeds, boiler pressure, and impurities mass content of weak phosphoric acid was studied.

Evaluation of the impurity profile of amino acids by means of CE.

The aim of this study was to develop a general approach for characterizing the impurity profile of amino acids at level 0.1% by means of capillary electrophoresis (CE). Checking a variety of labeling reagents revealed 9-fluorenylmethyl chloroformate to be favorable, due to the high stability of its derivatives and the fact that the reagent peaks do not interfere with the peaks of the impurities. After optimization, the method was sufficiently sensitive to evaluate impurities at a 0.1% level by UV detection. The method was representatively validated for phenylalanine (Phe) with regard to selectivity, precision, linearity and accuracy using model mixtures of potential impurities. The CE analyzes method was applied to Phe samples of different manufacturers and the capabilities of the strategy was also demonstrated by samples of tryptophan and serine.

The epigenetic toxicity of pyrene and related ozonation byproducts containing an aldehyde functional group.

Gap junction intercellular communication (GJIC) was used to assess the epigenetic toxicity of pyrene, pure byproducts of pyrene ozonation, and other compounds similar in chemical structure. Byproduct mixtures collected from HPLC were also evaluated using GJIC. Of the 11 pure compounds studied, five inhibited GJIC completely. Two inhibiting compounds contained four rings and were the only compounds studied with greater than three rings. The remaining three compounds contained either two or three rings, and all three contained an aldehyde group. Toxicological evaluation and GC/MS of impure byproduct mixtures showed that two common compounds were found in inhibiting fractions. These common compounds contained both a bay region and at least one aldehyde group.

High radiation from intrinsic and injected impurities in Tore Supra ergodic divertor plasmas

We report experiments aimed at comparing several impurity mixtures (C, O, Cl, N, Ne, Ar) regarding their capability to reduce the power load on the divertor target plates. The divertor conditions required for each mixture to minimise the parallel power flux are determined, along with the resulting core effective charge Z eff and volume averaged density. The radiation efficiency (ratio of edge radiation to plasma core contamination) of intrinsic carbon is found to increase with the total injected power. In the impurity injection experiments, nitrogen is found to be the best choice to reduce the power flux to the target plates: it has the same characteristics as C/O radiation (low core contamination), and it can be controlled. The low Z eff observed in this case is attributed to the large value of the screening of the radiating ionisation stages of the impurity.

Analysis of Impurities in Mixtures of West-Siberian Crude Oils

The content of B, Mg, Na, Al, P, V, Mn, Cu, Cr, Fe, Ni, Zn, Ag, Br, Sn, I, Ba, W, Pb, and Bi in 24 samples of industrial mixtures of West-Siberian oils was studied using the method of inductively coupled plasma with mass spectrometric registration.

Silicone Antifoam Performance: Correlation with Spreading and Surfactant Monolayer Packing

The relationship between the spreading of antifoam oils and their performance is much discussed in the literature, but a demonstrated connection between antifoam spreading and performance has been lacking. This paper reports the performance of a poly(dimethylsiloxane) (PDMS)-based antifoam on foam produced by 12 surfactant solutions. These include single or mixed surfactant systems, including impure surfactant mixtures to model fabric washing detergents. The oil film spreading pressure, πo/w, is presented as a simple and relevant measurement of the thermodynamics of antifoam oil spreading. Antifoaming efficacy was measured as the relative reduction in the initial foam height, ΔHrel, using cylinder shake tests at a fixed antifoam dosage. ΔHrel is shown to increase with πo/w, demonstrating a strong statistical correlation between antifoam oil spreading and its performance. Antifoam effectiveness varies with surfactant concentration, surfactant type, and surfactant hydrophobe size and also with increased density of surfactant packing. Surface shear viscosity, μs, was used to quantify surfactant packing. Antifoam effectiveness decreases with increasing surface shear viscosity. This finding provides a potentially useful link between antifoam efficacy and surfactant selection based on well-established surfactant molecular packing parameters. The role of spreading of antifoam oil at the air/surfactant solution interface is investigated. Oil film spreading pressure is shown to decrease by a power law function with increasing surface shear viscosity of the surfactant film. A new fluorescence technique was used to measure the extent of PDMS spreading. Initial results suggest a correlation between the spreading distance and antifoaming performance. An antifoam mechanism is proposed that features antifoam spreading as a direct contributor to bubble film rupture and incorporates surfactant type and concentration, surfactant packing density, and antifoam oil film spreading pressure as factors contributing to antifoam efficacy.

Investigation of ultrasound propagation in impurity-helium solids

The velocity and attenuation of ultrasound passing through porous impurity-helium solids immersed in liquid 4He have been measured in the temperature range 1.2–2.3 K. These solids were formed by injecting a mixture of impurity (Ne or N 2) and helium gases into superfluid 4He. We found that the speed of sound at low temperatures is close to that of first sound in bulk helium but decreases more rapidly with increasing temperature, similar to behavior observed in aerogel. The attenuation of sound in helium in the impurity-helium solids is bigger than in bulk helium and increases rapidly with temperature up to ∼1.8 K , after which a crossover to a much weaker temperature dependence was observed.

Investigations of Ultrasound Propagation in Porous Impurity-Helium Solids

The velocity and attenuation of ultrasound passing through porous impurity-helium solids immersed in liquid 4He have been measured in the temperature range 1.1–2.3 K. These solids were formed by injecting a mixture of impurity (e.g. D2, Ne, N2 or Kr) and helium gases into superfluid 4He. The sound signal seemed to propagate mainly in the helium contained in the pores, rather than through the solid sample itself. We found that the speed of sound at low temperatures is close to and decreases more rapidly with temperature than first sound in bulk helium, similar to behavior observed in aerogel. The attenuation of sound in helium in the “compressed” impurity-helium solids is bigger than in bulk helium and increases rapidly with temperature up to ∼1.65 K, after which a crossover to a much weaker temperature dependence was observed.