Argon Stream Research Articles

Nitrous oxide conversion in laminar premixed flames of CH4 + O2 + Ar

Experimental measurements of the adiabatic burning velocity in neat and NO formation in CH4+O2+Ar flames doped with small amounts of N2O are presented. The oxygen content in the oxidizer was varied from 15 to 17%. Non-stretched flames were stabilized on a perforated plate burner at 1atm. The Heat Flux method was used to determine burning velocities under conditions when the net heat loss of the flame is zero. Adiabatic burning velocities of methane+oxygen+argon mixtures were found in satisfactory agreement with the modeling. The NO concentrations in the flames doped with N2O (100ppm in the argon stream before mixing) were measured in the burnt gases at a fixed distance from the burner using probe sampling. Axial profiles of [NO] were found insensitive to the downstream heat losses. Experimental dependencies of [NO] versus equivalence ratio had a maximum between φ=1.1 and 1.2. Calculated concentrations of NO were in good agreement with the measurements. In lean flames calculated concentrations of NO strongly depends on the rate constant of reaction N2O+O=NO+NO if too high values proposed in the literature are employed. These new experimental data thus allowed for validation of the key reactions of the nitrous oxide mechanism of NO formation in flames.

Retinal Pigment Epithelium-Retinal G Protein Receptor-Opsin Mediates Light-dependent Translocation of All-trans-retinyl Esters for Synthesis of Visual Chromophore in Retinal Pigment Epithelial Cells

Visual perception begins with the absorption of a photon by an opsin pigment, inducing isomerization of its 11-cis-retinaldehyde chromophore. After a brief period of activation, the resulting all-trans-retinaldehyde dissociates from the opsin apoprotein rendering it insensitive to light. Restoring light sensitivity to apo-opsin requires thermal re-isomerization of all-trans-retinaldehyde to 11-cis-retinaldehyde via an enzyme pathway called the visual cycle in retinal pigment epithelial (RPE) cells. Vertebrates can see over a 10(8)-fold range of background illumination. This implies that the visual cycle can regenerate a visual chromophore over a similarly broad range. However, nothing is known about how the visual cycle is regulated. Here we show that RPE cells, functionally or physically separated from photoreceptors, respond to light by mobilizing all-trans-retinyl esters. These retinyl esters are substrates for the retinoid isomerase and hence critical for regenerating visual chromophore. We show in knock-out mice and by RNA interference in human RPE cells that this mobilization is mediated by a protein called "RPE-retinal G protein receptor" (RGR) opsin. These data establish that RPE cells are intrinsically sensitive to light. Finally, we show that in the dark, RGR-opsin inhibits lecithin:retinol acyltransferase and all-trans-retinyl ester hydrolase in vitro and that this inhibition is released upon exposure to light. The results of this study suggest that RGR-opsin mediates light-dependent translocation of all-trans-retinyl esters from a storage pool in lipid droplets to an "isomerase pool" in membranes of the endoplasmic reticulum. This translocation permits insoluble all-trans-retinyl esters to be utilized as substrate for the synthesis of a new visual chromophore.

Application of Electrochemical Reduction to Produce Metal Fuel Material from Actinide Oxides

The electrochemical reduction process has been recently developed for converting oxide nuclear fuels to metals. In order to characterize the reduction mechanism and to investigate appropriate conditions for improving the reduction rate, several reduction tests were conducted in a LiCl-Li2O electrolyte at 650°C using various types of cathode baskets containing 10 to 100 g of UO2. The reduction progressed from the outside to the center of the cathode basket, and the reduction rate might be determined by the transportation of oxygen ion to the bulk salt. It was verified that feeding in small UO2 particles and reducing the thickness of the UO2 layer in the cathode basket improved the reduction rate. The completion of UO2 reduction was indicated by the open circuit potential of the cathode basket exhibiting lithium deposition potential for a long time. A salt distillation test was conducted using the reduction product comprising a mixture of porous uranium metal particles and the electrolyte. The reduction product loaded in an yttria crucible was heated to 1400°C in an argon stream. The residue in the crucible consisted of a uranium metal ingot and a small amount of dross. The adhering LiCl seemed to be completely removed. Consequently, it was demonstrated in the electrochemical reduction followed by the salt distillation that a uranium metal ingot could be produced from the UO2 feed with a high degree of efficiency.

MSFIA system for mercury determination by cold vapour technique with atomic fluorescence detection

A new multisyringe flow injection analysis system for mercury determination using cold vapour technique assembling with atomic fluorescence spectrometry is proposed. The system consists of a multisyringe module as liquid driver, a gas–liquid separator, a gas dryer device and an atomic fluorescence detector. As reducing agent, 1% tin chloride solution is used. Standard solutions and carrier are prepared in 1% hydrochloric acid. An argon stream is employed as carrier gas for cold vapour technique. The development of the smart analytical system is feasible due to the four internal gains of the atomic detector and the versatility of software used. According to the signal obtained, the software is able to choose the most suitable internal gain for sample analysis. Four linear calibration curves (i.e. one for each internal gain) were obtained. The smart system developed allows to determine a wide concentration range from 120 to 0.006 μg L −1 Hg. The detection limit (3 σ/ S) achieved is 0.002 μg L −1. The relative standard deviation is inferior to 2% for each calibration curve. This system was validated by means of a solid reference material and it was applied to environmental samples successfully.

Laboratory Tests on Mercury Emission Monitoring with Resonating Gold-coated Silicon Cantilevers

To measure extremely low concentrations of mercury vapor in gases as encountered in flue gases of coal-fired power plants, accurate and reliable online and/or portable mercury detection systems are needed. As discussed in this communication, resonating silicon-based cantilevers coated with thin films of gold change their resonant frequency when exposed to mercury vapors and could serve as the basis for such sensing devices. Two different types of commercial AFM cantilevers, which differed by physical dimensions and surface finish, were coated with a 10 nm film of gold and were tested in streams of argon containing mercury. The argon flow rates ranged from 5.7 to 57.4 ml/min, carrying mercury vapors at concentrations between 37 and 700 microg/m3. The results show that smaller cantilevers (approximately 140 microm x 40 microm x 4 microm) with a resonant frequency of 270-275 kHz were sensitive to less than 10 picograms of mercury, whereas larger cantilevers (approximately 245 microm x 50 microm x 7 microm) with a resonant frequency of 155-165 kHz have a sensitivity about 10 times lower. The results indicate that the kinetics of mercury capture by the gold coating follows a simple power law-correlation with the mass change (delta m) being proportional to t(n), where t is the capture time and n depends strongly on the concentration of mercury in the gas. It is also demonstrated that the mercury can be stripped off the gold coating by heating to 350 degrees C, which would allowthe cantilevers to be regenerated and reused.

Particle Morphology of Various SiC-Based Nanocomposite Powders Made by the Aerosol-Assisted Synthesis Method

Herein, we present a part of a study on the preparation of SiC-based composite nanopowders by the two-stage Aerosol-Assisted Vapor Phase Synthesis (AAVS) method from organosilicon precursors (neat hexamethyldisiloxane, neat tetramethoxysilane, ethanol solutions of polydimethylsiloxane). Upon generation, liquid aerosol droplets were transported in a stream of argon through a ceramic reactor tube maintained at 1200 degrees C. The resulting solid by-products were collected on a nylon filter as bulk powders. Each raw powder was, subsequently, pyrolyzed in a furnace reactor heated to 1650 degrees C under a flow of argon. After the final pyrolysis at 1650 degrees C, mostly nanocrystalline silicon carbide powder with small quantities of free excess carbon was obtained from the neat hexamethyldisiloxane system, composite powder of not fully converted silica and SiC was prepared from the neat tetramethoxysilane system, and C-rich/SiC composite was made from the ethanol/polydimethylsiloxane solution system. The prevailing phase of the SiC component was the regular beta-SiC polytype. Most of the powders were composed of spheroidal particles--morphology imprinted during aerosol generation at 1200 degrees C and not much affected by the second-stage bulk pyrolysis at 1650 degrees C. The specifics of spheroidal morphology were characteristic of the applied precursor system.

Utilization of Waste Plastic for the Production of Metallic Iron, Hydrogen and Carbon Monoxide without Generating Carbon Dioxide

National legislation within Japan has increased the need for the development of new process technologies that will utilise various waste materials. The present study is aimed at generating some fundamental data with respect to the application of waste plastic as a potential reductant for iron oxide. By using a high frequency induction furnace, mixtures of polyethylene+Fe2O3 were heated very rapidly to temperatures between 1673 and 2073 K in a stream of argon. Gas chromatography, chemical analysis and X-ray diffraction were used to detect reaction products, which consisted of metallic iron, ferrous oxide, char, CO, CO2, H2O, H2 and CH4, depending upon C/O mole ratios within the polyethylene+Fe2O3 mixture and the experimental temperature. The results were in good agreement with values calculated from thermodynamic equilibrium.

Hydrogen Release Rate of SUS316 in Ar Gas Flow and Vacuum

To understand the mechanism of hydrogen release from materials used in vacuum technology, the release behavior of tritium from stainless steel SUS316 previously loaded with this gas was investigated isothermally at 423 K either under a stream of argon or under vacuum conditions. Depth profiles of the heated specimens were determined by chemical etching. The experimental release rate and the tritium depth profile in the solid could be simulated with a model based on bulk diffusion. The diffusion coefficients used to fit the depth profiles of specimens heated under vacuum at 423 K were non-discernible from those obtained with specimens heated under a stream of Ar at the same temperature.

The High‐Temperature Alicyclic Ring Contraction of 1,1‐Dichloroperfluorotetralin and the Alicyclic Ring Opening of 1,1‐Dichloroperfluorobenzocyclobutene.

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An attempt to improve electrical conductivity of the pyrolysed carbon-LiMn 2O 4− yS y (0 ≤ y ≤ 0.5) composites

An attempt to obtain conductive carbon layer (CCL) on the LiMn 2O 4 and LiMn 2O 4− y S y spinels, using the radical precipitation polymerization of acrylonitrile (AN) and styrene–acrylonitrile (SAN) in water suspension of the spinels followed, by pyrolysis of the composed precursors was made. In the case of PAN–spinel precursors the CCL on spinel particles was effectively formed. Phase transitions, as well as thermal and electrical properties of the carbon-sulphided spinel composites were characterized. An attempt with SAN copolymer failed due to the reaction between SAN and the spinels during pyrolysis, even in the argon stream.

The high-temperature alicyclic ring contraction of 1,1-dichloroperfluorotetralin and the alicyclic ring opening of 1,1-dichloroperfluorobenzocyclobutene

The pyrolysis of 1,1-dichloroperfluorotetralin ( 4) in a stream of argon gives a mixture contained perfluoro-1-methyleneindan ( 1), perfluoro-3-methylindene ( 6), 1,1-dichloroperfluoroindan ( 2) and perfluoroindene ( 7), while copyrolysis of tetralin 4 with CHClF 2 gives a mixture of compounds 1, 6 in the absence of compounds 2 and 7. 1-Chloro-2-(1-chloro-2,2-difluorovinyl)-3,4,5,6-tetrafluorobenzene ( 12) is formed in the pyrolysis of 1,1-dichloroperfluorobenzocyclobutene ( 5) in a stream of argon as well as in a stream of CHClF 2.

Coating of a thin layer of NaBH4 solution for mercury vapor generation coupled to atomic fluorescence spectrometry

Sodium tetrahydroborate (NaBH4) was, for the first time, coated onto PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene propylene), Excelon (microline) and PEEK (polytetrafluoroethylene) surfaces and used for mercury vapor generation-atomic fluorescence spectrometric determination. A lab-on-valve (LOV) incorporating a miniature membrane phase separation chamber was employed to facilitate the operation. A 600–1200 nm thin film of NaBH4 solution was coated onto the interior surface of tubes by sweeping through 30 μl of NaBH4 solution with an argon stream. Mercury cold vapor was generated as sample solution flowing through the pre-coated tubing carried by argon. The film coating was renewed for each operating run. The vapor was either immediately excited in the outlet of the separator in the LOV and detected by directing the fluorescence to a photomultiplier with optical fibers, or directed to a commercial AFS-920 atomic fluorescence spectrometer. NaBH4 coating not only minimized fluorescence quenching by concomitant hydrogen encountered in conventional AFS, but the coating process also effectively eliminated mercury memory effects. In addition, the coating substantially simplified the operation of vapor generation using a single syringe pump for fluidic delivery. When using PTFE tubing as a coating medium, limits of detection of 0.06 and 0.005 μg l−1 were derived by monitoring with a LOV-AFS system and an AFS-920 spectrometer, respectively, with a sample volume of 500 μl. A sampling frequency of 60 h−1 along with RSDs of 2.9% and 2.0% at 2.0 μg l−1 were achieved. Mercury contents in certified reference materials and a local coastal seawater were measured.

Utilization of Waste Wood for Production of Iron, Carbon Monoxide and Hydrogen without generating Carbon Dioxide

National legislation within Japan has increased the need for the development of new process technologies that will utilise waste wood materials. The present study is aimed at generating some fundamental data with respect to the reduction of iron oxide by waste wood. By using a high frequency induction furnace, mixtures of wood + Fe2O3 were heated very rapidly to temperatures between 1673 and 2073K in a stream of argon. Gas chromatographic technique applied on exhaust gases escaping from the furnace revealed that the gaseous reaction products consisted mainly of carbon monoxide and hydrogen. On the other hand, conventional chemical analysis and X‐ray diffraction technique made on condensed‐phase reaction products detected the presence of Fe‐C alloys, solid carbon (char) and ferrous oxide, depending upon the atomic ratio of C/O within wood + Fe2O3 mixture. Thus, the reaction products consisted of metallic iron, ferrous oxide, char, CO, CO2, H2O, H2 and CH4, depending upon C/O atomic ratio within the mixture and the experimental temperature. The results were in good agreement with values calculated from thermodynamic equilibrium.

Ni–Re intermetallic oxygen getters

Two binary intermetallic compounds PrNi 5 and Nd 2Ni 17 have been tested as getters for reducing the oxygen content in a stream of pure argon. Both the intermetallics used are the Ni richest phase in the respective rare-earth (RE)-Ni phase diagrams. The gettering efficiency has been evaluated through the quantities MTGA and OPP g. The former is the minimum temperature of the getter activity, i.e., the temperature at which the gettering action becomes detectable, and OPP g is the oxygen partial pressure in the gas stream after reaction. The best MTGA values found are 242 and 287 °C for PrNi 5 and Nd 2Ni 17, respectively, with OPP g minimum values equal to 1×10 −16 and 1×10 −15 Pa. Though these values are produced for a relatively short time, the average OPP g values are satisfactory for practical purposes. It has been shown that the oxidation produces the rare-earth oxide (RE 2O 3) and Ni. The rate-determining step has been found to be the transport of oxygen in the gas phase and its transport constant has been also calculated.

Flow system for pre-concentration and spectrophotometric determination of reactive mercury

A new flow system to pre-concentrate and determine reactive mercury in effluents by photometry is presented. The system is based on the reduction of the reactive mercury present in a 500 mL sample with a Sn(II) solution. The reduced mercury is swept out by an argon stream and carried to a straight glass tube (60 cm long, 3 mm i.d.) inclined in an angle of 15º. The inner surface of this tube has been previously covered by a renewable liquid layer of an oxidant solution containing H2O2 (12%, m/v) and HNO3 (3.0 mol L-1) produced after introduction and passage of a liquid monosegment containing those reagents. The swept Hg0 undergoes an oxidative process and the Hg(II) formed is retained in the layer. After a 10 min sweep time interval the argon flow is stopped and a reagent monosegment (350 µL) containing PAR [4-(2-pyridylazo)resorcinol], 1.0 x 10-3 mol L-1, in an ammonia/ ammonium chloride buffer (4.0 mol L-1; pH 9.0) is introduced and passes through the glass tube. A strongly coloured complex between PAR and Hg(II) is formed and carried to the detection system composed of a light emitting diode (LED, lambdamax = 525 nm) and a photodiode detector. Sample processing time is about 12 min. The system is washed and a fresh liquid layer is formed, preparing the system for a new determination. This method concentrates the sample by a factor of 148 and achieves a detection limit of 0.16 µg L-1.

Determination of free and total sulfur dioxide in wine samples by vapour-generation inductively coupled plasma–optical-emission spectrometry

Sulfur dioxide (SO(2)) is used as a preservative and stabilizer in wine production to prevent undesired biochemical processes in the must and the final product. The concentration of SO(2) is restricted by national regulations. There are two main forms of SO(2) in wine-free (inorganic forms) and bound (fixed to organic compounds, e.g. aldehydes). Iodometric titration is commonly employed for determination of SO(2) concentration (either by direct titration or after pre-separation by distillation); other techniques are also used. In this work inductively coupled plasma-optical-emission spectrometry with vapour generation was used for determination of free and total SO(2) in wine. Gaseous SO(2) is released from the sample by addition of acid and swept into the ICP by an argon stream. The intensity of the sulfur atomic emission lines is measured in the vacuum UV region. Determination of total SO(2) is performed after hydrolysis of bound forms with sodium hydroxide (NaOH). Concentrations of acid for vapour generation and NaOH for hydrolysis were optimised. The method was used for determination of free and total SO(2) in red and white wine samples and results were compared with those from iodometric titration.

Experimental Investigation of the Interaction between an Electric Arc and a Gas Flow

The results of investigating the shape of an electric arc carrying an electric current of less than 100 A and exposed to an air, nitrogen, or argon stream at a stream velocity of from zero to 20 m/s, when the interelectrode gap is less than 20 mm, are reported. The shape of the arc is qualitatively investigated as a function of the gas type, blowing velocity, and interelectrode gap. It is shown that an arc burning in a channel with insulated walls is much more stable under these conditions than an arc with the same parameters burning in free space.

Endothelial lipase releases saturated and unsaturated fatty acids of high density lipoprotein phosphatidylcholine

We assessed the ability of endothelial lipase (EL) to hydrolyze the sn-1 and sn-2 fatty acids (FAs) from HDL phosphatidylcholine. For this purpose, reconstituted discoidal HDLs (rHDLs) that contained free cholesterol, apolipoprotein A-I, and either 1-palmitoyl-2-oleoylphosphatidylcholine, 1-palmitoyl-2-linoleoylphosphatidylcholine, or 1-palmitoyl-2-arachidonylphosphatidylcholine were incubated with EL- and control (LacZ)-conditioned media. Gas chromatography analysis of the reaction mixtures revealed that both the sn-1 (16:0) and sn-2 (18:1, 18:2, and 20:4) FAs were liberated by EL. The higher rate of sn-1 FA cleavage compared with sn-2 FA release generated corresponding sn-2 acyl lyso-species as determined by MS analysis. EL failed to release sn-2 FA from rHDLs containing 1-O-1'-hexadecenyl-2-arachidonoylphosphatidylcholine, whose sn-1 position contained a nonhydrolyzable alkyl ether linkage. The lack of phospholipase A(2) activity of EL and its ability to liberate [(14)C]FA from [(14)C]lysophosphatidylcholine (lyso-PC) led us to conclude that EL-mediated deacylation of phosphatidylcholine (PC) is initiated at the sn-1 position, followed by the release of the remaining FA from the lyso-PC intermediate. Thin-layer chromatography analysis of cellular lipids obtained from EL-overexpressing cells revealed a pronounced accumulation of [(14)C]phospholipid and [(14)C]triglyceride upon incubation with 1-palmitoyl-2-[1-(14)C]linoleoyl-PC-labeled HDL(3), indicating the ability of EL to supply cells with unsaturated FAs.

WC/Co 초경 스크랩 산화물의 고체탄소에 의한 환원/침탄

In the present study, the focus is on the analysis of carbothermal reduction of oxide powder prepared from waste WC/Co hardmetal by solid carbon under a stream of argon for the recycling of the WC/Co hard-metal. The oxide powder was prepared by the combination of the oxidation and crushing processes using the waste <TEX>$WC-8 wt.\%Co$</TEX> hardmetal as the raw material. This oxide powder was mixed with carbon black, and then this mixture was carbothermally reduced under a flowing argon atmosphere. The changes in the phase structure and gases discharge of the mixture during carbothermal reduction was analysed using XRD and gas analyzer. The oxide powder prepared from waste <TEX>$WC-8wt.\%Co$</TEX> hardmetal has a mixture of <TEX>$WO_{3} and CoWO_{4}$</TEX>. This oxide powder reduced at about <TEX>$850^{\circ}C$</TEX>, formed tungsten carbides at about <TEX>$950^{\circ}C$</TEX>, and then fully transformed to a mixed state of tungsten carbide (WC) and cobalt at about <TEX>$1100^{\circ}C$</TEX> by solid carbon under a stream of argon. The WC/Co composite powder synthesized at <TEX>$1000^{\circ}C$</TEX> for 6 hours from oxide powder of waste <TEX>$WC-8wt.\%Co$</TEX> hardmetal has an average particle size of <TEX>$0.3 {\mu}m$</TEX>.

Substrate Specificity, Localization, and Essential Role of the Glutathione Peroxidase-type Tryparedoxin Peroxidases in Trypanosoma brucei

Trypanosoma brucei, the causative agent of African sleeping sickness, encodes three nearly identical cysteine homologues of the classical selenocysteine-containing glutathione peroxidases. Although one of the sequences, peroxidase III, carries both putative mitochondrial and glycosomal targeting signals, the proteins are detectable only in the cytosol and mitochondrion of mammalian bloodstream and insect procyclic T. brucei. The enzyme is a trypanothione/tryparedoxin peroxidase as are the 2 Cys-peroxiredoxins of the parasite. Hydrogen peroxide, thymine hydroperoxide, and linoleic acid hydroperoxide are reduced with second order rate constants of 8.7 x 10(4), 7.6 x 10(4), and 4 x 10(4) m(-1) s(-1), respectively, and represent probable physiological substrates. Phosphatidylcholine hydroperoxide is a very weak substrate and, in the absence of Triton X-100, even an inhibitor of the enzyme. The substrate preference clearly contrasts with that of the closely related T. cruzi enzyme, which reduces phosphatidylcholine hydroperoxides but not H(2)O(2). RNA interference causes severe growth defects in bloodstream and procyclic cells in accordance with the peroxidases being essential in both developmental stages. Thus, the cellular functions of the glutathione peroxidase-type enzymes cannot be taken over by the 2 Cys-peroxiredoxins that also occur in the cytosol and mitochondrion of the parasite.