Chemical Reaction

Precolumn high-performance liquid chromatography derlvatlratlon of several vinyl aldehydes, speclflcally acrolein, crotonaldehyde, and methacroleln, has been studied by use of the reagent anthrone. After selective condensation of these a-or @-unsaturated aldehydes to form fluorescent benranthrone derivatives, separation of these compounds was facile on a 10-cm C-18 column. Although ultravldet detectlon was posslble, fluorescent detection proved more versatile and sensitive. Four liquor samples were subsequently assayed for acrolein and crotonaldehyde. Linearity for these compounds In alcohollc solutions ranged from 0.02 to at least 14 ppm wlth detection limits reaching down to 0.005 ppm.

DNA computing is a new computing paradigm which uses bio-molecular as information storage media and biochemical tools as information processing operators. It has shows many successful and promising results for various applications. Since DNA reactions are probabilistic reactions, it can cause the different results for the same situations, which can be regarded as errors in the computation. To overcome the drawbacks, much works have focused to design the error-minimized DNA sequences to improve the reliability of DNA computing. In this research, Population-based ACO (P-ACO) is proposed to solve the DNA sequence optimization. P-ACO approach is a meta-heuristic algorithm that uses some ants to obtain the solutions based on the pheromone in their colony. The DNA sequence design problem is modelled by four nodes, representing four DNA bases (A, T, C, and G). The results from the proposed algorithm are compared with other sequence design methods, which are Genetic Algorithm (GA), and Mult...

The crosslinking of the unsaturated polyester was studied by using experiments and a model of the process. The kinetic parameters were calculated from the heat flux-time curves obtained by differential scanning calorimetry (DSC, Netzsch-Simultaneous Thermal Analyser DSC 200), working in DSC (dynamic) mode. The temperature-time histories were studied in plain sheet copper mould. The mathematical model was constructed by taking into account the heat transferred by conduction through the resin, as well as the kinetics of heat generated by the crosslinking reaction. The contributions to the rise in temperature from heat conduction and chemical reaction are different in different parts of the composite, and can explain the temperature-, or degree of crosslinking (DOC)time histories. By considering temperature-time histories developed within the sample, more extensive knowledge of the process can be obtained. The effect of the heat transfer by conduction through the composite as well as the internal heat generated by the cure reaction is clearly shown, despite the complexity of the process. Finally, good agreement between experimental data and predicted mathematical model of the crosslinking process in plane sheet mould was shown.

We investigated the wetting behavior and reactions of different metals on Si3N4 using sessile drop measurements, analysis of reaction layers, and measuremeints of strengths of joined bars. Active metals, such as A1 and Ti, and alloys that contain them react with Si3N4 and cause ,wetting and spreading at the interface. AI-Si3N4 reaction at 900°C produced a thin layer of A1203 at the interface. Reaction between Si3N4 and Ag-Cu-Ti braze alloys at 900°C resulted in a complex microstructure in the reaction zone that contained TIN and titanium silicides. Breaking strengths of Si3N4 bars joined with the Ag-Cu-Ti braze alloys were higher than those for Si3N4 joined with Al, primarily because of the better wetting by the Ag-Cu-Ti alloys. Nonreactive metals and alloys such as Sn, In, Ag-Cu, and Ag-Cu-Sn neither wet, spread, nor adhere to Si3N4 substrates. [

This paper reports on the preparation of titanium (IV) oxide films via the improved atmospheric pressure barrier torch discharge (BTD) deposition. This approach is a modification of the atmospheric pressure glow discharges (APGDs) ranking among plasma enhanced chemical vapor deposition (PECVD) techniques. These methods are based on plasma-chemical reactions of the precursors' vapors occurring in the active plasma environment. The layers are produced in terms of heterogeneous recombination reactions of the high active species on the supporting surface. The major treated topic comprises the influence of the used support on the physical properties of the layers. A set of three different supports was used including quartz slides (nonconducting, dielectric), silicon discs (semi-conducting) and polished Ni sheets (conducting). Crystallographic structure, surface roughness, surface wettability and the film thickness were assessed and used as a set of physical properties to be discussed and compared for each of the films and mutually. In parallel the qualitative analysis of the emission spectra of the barrier torch discharge during the deposition process was also presented. Different conductive connection of plasma stream with the substrate crucially influences the temperature of this substrate. It has a direct effect mainly on the crystallinity and morphology of the films and also on the plasma parameters. This knowledge might be used as a tool for the optimization of deposition conditions. Photocatalytic functionality of the layers was quantified in a simple test based on the photocatalytic oxidation of Rhodamine B (C 28 H 31 ClN 2 O 3 ) under UV radiation.

Thiobacillus denitrijicans is a strictly autotrophic and facultative anaerobe first described in detail by Baalsrud and Baalsrud. ' Under anaerobic conditions nitrate may be used as a terminal electron acceptor with reduction to elemental nitrogen. Thiosulfate, elemental sulfur, and sulfide may be used as energy sources with oxidation to sulfate; however, sulfide is an inhibitory substrate. Sublette and S y l v e~t e r~.~ have demonstrated that T. denitrijicans may be readily cultured anaerobically in batch and continuous reactors on H2S(g) under sulfide limiting conditions. Under these conditions sulfide concentrations in the culture medium were less than IpM resulting in very low concentrations in the reactor outlet gas (less than 0.05pM). The stoichiometry of the anaerobic oxidation of H2S(g) in batch and continuous cultures was reported and stable reactor operation demonstrated at reactor loadings as high as 4-5 mmol H2S oxidized/h/g biomass. Maximum H2S loading of the biomass was estimated at 5.4-7.7 mmol H2S/h/g biomass under sulfide limiting conditions. Sublette and S y l v e~t e r~,~ have proposed a process for the microbial desulfurization of natural gas based on the oxidation of H2S(g) by Thiobacillus denitrijicans. The proposed process could be greatly simplified if aseptic operation of the reactor was not required. Accordingly, we report here a study of the effects of heterotrophic contaminants on H2S(g) oxidation by T. denitrijicans.

Pulsatile action can be used to mix two streams entering a tube from two separate branches of a bifurcation at low Reynolds numbers. The pulsatile action is provided by two pinch valves, which deform flexible tubing immediately upstream of the connection. The pinch valve action is controlled using a master-slave pulse generator setup. The quality of mixing is evaluated directly by measuring the fluorescence that results from the chemical reaction of species transported in the two streams, one containing native biotin and the other, fluorescein biotin bound to streptavidin. The reaction kinetics are accounted for by normalization using fluorescence measurements on well mixed solutions at the same residence time. The results show that the pulsatile micromixer provides almost complete mixing. Furthermore, the present measurements match results obtained in a previous experiment where flow visualization and image analysis were used to measure mixing quality in a scaled-up model.

We have developed a methodology for including effects of chemical reactions in coarse-grained computer simulations such as those that use the united atom approximation. The new coarse-grained chemical reaction model (CGCRM) adopts the philosophy of kinetic Monte Carlo approaches and includes a probabilistic element to predicting when reactions occur, thus obviating the need for a chemically correct interaction potential. The CGCRM uses known chemical reactions along with their probabilities and exothermicities for a specific material in order to assess the effect of chemical reactions on a physical process of interest. The reaction event in the simulation is implemented by removing the reactant molecules from the simulation and replacing them with product molecules. The position of the product molecules is carefully adjusted to make sure that the total energy change of the system corresponds to the reaction exothermicity. The CGCR model has been applied to simulations of laser irradiation of chlorobenzene at fluences such that there is ablation or massive removal of material. Two simulations, one for photothermal ablation and one for photochemical ablation, are compared to each other and to experimental data. In the photothermal simulation, all the laser energy goes into heat. In the photochemical simulation, the photon cleaves the C-Cl bond creating two radicals that can undergo subsequent abstraction and radical-radical recombination reactions.

Proper mixing of reagents is of paramount importance for an efficient chemical reaction. While on a large scale there are many good solutions for quantitative mixing of reagents, as of today, efficient and inexpensive fluid mixing in the nanoliter and microliter volume range is still a challenge. Complete, i.e., quantitative mixing is of special importance in any small-scale analytical application because the scarcity of analytes and the low volume of the reagents demand efficient utilization of all available reaction components. In this paper we demonstrate the design and fabrication of a novel centrifugal force-based unit for fast mixing of fluids in the nanoliter to microliter volume range. The device consists of a number of chambers ͑including two loading chambers, one pressure chamber, and one mixing chamber͒ that are connected through a network of microchannels, and is made by bonding a slab of polydimethylsiloxane ͑PDMS͒ to a glass slide. The PDMS slab was cast using a SU-8 master mold fabricated by a two-level photolithography process. This microfluidic mixer exploits centrifugal force and pneumatic pressure to reciprocate the flow of fluid samples in order to minimize the amount of sample and the time of mixing. The process of mixing was monitored by utilizing the planar laser induced fluorescence ͑PLIF͒ technique. A time series of high resolution images of the mixing chamber were analyzed for the spatial distribution of light intensities as the two fluids ͑suspension of red fluorescent particles and water͒ mixed. Histograms of the fluorescent emissions within the mixing chamber during different stages of the mixing process were created to quantify the level of mixing of the mixing fluids. The results suggest that quantitative mixing was achieved in less than 3 min. This device can be employed as a stand alone mixing unit or may be integrated into a disk-based microfluidic system where, in addition to mixing, several other sample preparation steps may be included. Physics 80, 075102-1 075102-2 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-3 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-5 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-6 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-7 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒

communities, values of b i,j were selected from uniform distributions between 0 and 20.1 (plant-plant competition), 20.3 (herbivores ! plants; that is, the effect of herbivores on plants), 0.1 (plants ! herbivores), 20.1 (predators ! herbivores), and 0.05 (herbivores ! predators). Intraspecific interactions were selected at random between 20.1 and 20.2 for plants, and set to 20.2 for herbivores and predators. For competitive communities, interspecific values of b i,j were selected uniformly between 0 and 20.1, and intraspecific values between 20.06 and 20.16. For the arbitrary topology, the probability of any pair of species interacting was 0.5, and of the interacting pairs of species 45% were competitors, 45% were prey and predators, and 10% were mutualists. The magnitudes of interspecific values of b i,j were selected uniformly between 0 and 0.1, with sign dictated by type of interaction, and intraspecific values were selected between 20.06 and 20.16.

It was reported recently that aniline in the presence of ammonia was converted to picolines over zeolite catalysts. The picolines are important intermediates in the dye and resins industries. However, no report has appeared on the reactions of arylamines over zeolites despite the fact that nitrogen heterocycles make up part of the structure of oil shale kerogens. The thermal arrangement of N-alkylaniline hydrochlorides in a sealed tube to give ringalkylated anilines has long been known as the Hoffmann-Martius rearrangement. In this note, the authors describe the rearrangement of N-methylaniline involving a methyl-N bond cleavage to ring-alkylated anilines and N-methylation to N, N-dimethylaniline over H-ZSM-5, H-Theta-1 and H-Y zeolites.

We report on the direct measurement of the dynamics of water molecules in the solvation shell of an ion in aqueous solution. The hydrogen-bond dynamics of water molecules solvating a Cl Ϫ , Br Ϫ , or I Ϫ anion is slow compared with neat liquid water, indicating that the aqueous solvation shells of these ions are rigid. This rigidity can play an important role in the overall dynamics of chemical reactions in aqueous solution. The experiments were performed with femtosecond midinfrared nonlinear spectroscopy, because this technique allows the spectral response of the water molecules in the solvation shell to be distinguished clearly from that of the other water molecules in the solution.

Autohydrolysis and dilute-acid hydrolysis were used as pretreatment methods to enhance the enzymatic digestibility of cellulose in two different lignocellulosic substrates, a softwood mixture and an agricultural residue of almond shells. The changes in the chemical composition of the softwood mixture during dilute-acid pretreatment were studied, and the results were grouped by using a severity parameter, KR OH , which was derived from the kinetics of hemicellulose solubilization. The average degree of polymerization of the cellulose retained in the pretreated substrate, DP v , was investigated and its trend compared with that of almond shells. Cellulose DP v decreased for both the substrates from a value of 700 for the untreated lignocellulosic to around 200, which corresponds to the leveling-off degree of polymerization, as there is no significant variation in DP v when severity increases. Glucose yields after enzymatic saccharification of the pretreated substrates turned out to be higher for almond shells than for the softwood mixture, which had a very low susceptibility to enzymatic hydrolysis throughout the spectrum of experimental conditions investigated. At KR OH ) 15 000, the glucose yield for the softwood mixture is 44% of the potential fraction present in the pretreated pulp, while for almond shells the maximum yield surpasses 97% for KR OH ) 3. The different behavior between these lignocellulosic species is not caused by different degrees of cellulose depolymerization nor by the removal of different amounts of carbohydrates during pretreatments in equivalent conditions.

The mass transfer around a rising bubble has been studied within the field of glass melting processes. Due to the large value of liquid viscosity, creeping flow was used. The rising bubble is assumed to have a clean interface with a total mobility and the exact solution of Hadamard or Rybczynski was used to define the velocity field around the bubble. The mass transfer of oxygen in the soda-lime-silica glass melt where oxidation-reduction reactions of iron oxides occur is also described. The dimensionless mass transfer coefficient, Sherwood number, was determined as a function of the Péclet number based on the terminal rise velocity of the bubble. Two different techniques have been used: the first based on the boundary layer theory and the second using a finite element method. In order to take into account the oxidation-reduction reaction in a unified framework, a modified Péclet number has been defined as a function of two dimensionless numbers. The first is strongly linked to the equilibrium constant of the chemical reaction and the second is the glass saturation, defined as the ratio of oxygen concentration in the bulk to that at the bubble surface. The Sherwood number, taking into account the chemical reactions, increases with iron content as well as with glass reduction (i.e. small saturation level). From an application point of view, the determination of a modified Péclet number is important because it is possible to use a similar expression (determined without the reaction) by replacing the classical Péclet number by the modified one proposed herewithin.

Aromatic amines represent one of the most important classes of industrial and environmental chemicals: many of them have been reported to be powerful carcinogens and mutagens, and/or hemotoxicants. Their toxicity has been studied also with quantitative structure-activity relationship (QSAR) methods: these studies are potentially suitable for investigating mechanisms of action and for estimating the toxicity of compounds lacking experimental determinations. In this paper, we first summarized the QSAR models for the rodent carcinogenicity of the aromatic amines. The gradation of potency of the carcinogenic amines depended firstly on their hydrophobicity, and secondly on electronic (reactivity, propensity to be metabolically transformed) and steric properties. On the contrary, the difference between carcinogenic and non-carcinogenic aromatic amines depended mainly on electronic and steric properties. These QSARs can be used directly for estimating the carcinogenicity of aromatic amines. A two-step prediction is possible: (1) estimation of yes/no activity; (2) if the answer from step 1 is yes, then prediction of the degree of potency. The QSARs for rodent carcinogenicity were put in a wider context by comparing them with those for: (a) Salmonella mutagenicity; (b) general toxicity; (c) enzymatic reactions; (d) physical-chemical reactions. This comparative QSAR exercise generated a coherent global picture of the action mechanisms of the aromatic amines. The QSARs for carcinogenicity were similar to those for Salmonella mutagenicity, thus pointing to a similar mechanism of action. On the contrary, the general toxicity QSARs (both in vitro and in vivo systems) were mostly based on hydrophobicity, pointing to an aspecific mechanism of action much simpler than that for carcinogenicity and mutagenicity. The oxidation of the amines (first step in the main metabolic pathway leading to carcinogenic and mutagenic species) had identical QSARs in both enzymatic and physical-chemical systems, thus providing evidence for the link between simple chemical reactions and those in biological systems. The results show that it is possible to generate mechanistically and statistically sound QSAR models for rodent carcinogenicity, and indirectly that the rodent bioassay is a reliable source of good quality data.

This research demonstrated the possibility of achieving conversions above the original equilibrium conversion based on the feed conditions by combining the selective separation effect of a membrane and the catalytic function of transition metals. A catalytic membrane reactor, containing a tubular Vycor glass membrane which was impregnated with a platinum catalyst, was studied with the model reaction of cyclohexane dehydrogenation. The equilibrium shift was significant for the operation with high space time. Numerical simulations using a single-cell model showed good agreements with experimental data. The performance of the catalytic membrane reactor was theoretically compared with that of a reactor consisting of an inert tubular Vycor glass membrane and catalyst pellets in the feed-side chamber. The result showed that the catalytic membrane reactor was superior to the inert membrane reactor for the operation with high space time but was less effective for the operation with low space time.

The influence of human whole saliva on selected alcohols, aldehydes, 3-alkyl-2-methoxypyrazines, and phenols in food-relevant concentrations was investigated. At pH 7.5-8 it was found that the alcohols, methoxyphenols, methoxypyrazines, and 3-hydroxy-4,5-dimethyl-2(5H)-furanone remained unmodified by saliva, whereas aldehydes were reduced to their corresponding alcohols. Generally, the processes were found to be dependent on the salivary activity of the panelists as well as on the concentration of the applied odorants. Reduction of the aldehydes did not occur after thermal treatment of the saliva. These investigations are aimed at finding an explanation for longer lasting aftertaste in humans, as it is induced by some odor-active compounds after the consumption of food materials.

The storage of large volumes of industrial CO 2 emissions in deep geological formations is one of the most promising climate mitigation options. The long-term retention time and environmental safety of the CO 2 storage are defined by the interaction of the injected CO 2 with the reservoir fluids and rocks. Finding a storage solution that is long lasting, thermodynamically stable and environmentally benign would be ideal. Storage of CO 2 as solid magnesium or calcium carbonates in basaltic rocks may provide such a long-term and thermodynamically stable solution. Basaltic rocks, which primarily consist of magnesium and calcium silicate minerals, provide alkaline earth metals necessary to form solid carbonates. In nature, the carbonization of basaltic rocks occurs in several well-documented settings, such as in the deep ocean crust, through hydrothermal alteration and through surface weathering. The goal of the CarbFix pilot project is to optimize industrial methods for permanent storage of CO 2 in basaltic rocks. The objective is to study the in-situ mineralization of CO 2 and its long term fate. The project involves the capture and separation of flue gases at the Hellisheidi Geothermal Power Plant, the transportation and injection of the CO 2 gas fully dissolved in water at elevated pressures at a depth between 400 and 800 m, as well as the monitoring and verification of the storage. A comprehensive reservoir characterization study is on-going prior to the CO 2 injection, including soil CO 2 flux measurements, geophysical survey and tracer injection tests. Results from the tracer tests show significant tracer dispersion within the target formation, suggesting large surface area for chemical reactions. The large available reservoir volume and surface area in combination with relatively rapid CO 2 -water-rock reactions in basaltic rocks may allow safe and permanent geologic storage of CO 2 on a large scale.

The lifetimes and relative quantum yields of the three fluorescence components of the PI (red-absorbing) form of 124-kDa oat phytochrome in H 2 0 and D 2 0 solutions have been determined by single-photon-timing techniques. Lifetime and quantum yield of the main component, which is the shortest lived (about 40 ps a t low concentration) and reflects the photochromic properties of P,, are not affected by D20. The medium-lifetime component (about 180 ps at low concentration), which is attributable to a photochromic source behaving comparable to that responsible for the main component, is not affected

Metal dispersion and support effects on Fischer-Tropsch synthesis rate and selectivity were studied at conditions that favor the information of C 5 + hydrocarbons (> 80% selectivity). On Ru, these effects are minor for the supports (SiO 2 , Al 2 O 3 , TiO 2 ) and the dispersion range ...

Summary. Two model compounds, n-dodecylpyridinium bromide (n-DDPB) and 1-octyn-3-ol, were tested in HCl acid as inhibitors for J55 oilfield stee. This paper describes the kinetic and chemical analyses conducted to arrive at inhibition mechanisms for these model compounds. These studies show that the pyridinium forms a weak bond with the chloride-covered surface an is sensitive to temperature and [HCl]. Octynol, however, chemisorbs and produces a film that contains a reaction product of the acetylenic alcohol. This film is quite insensitive to changes in temperature and [HCI]. Introduction The stimulation of oil and gas wells with concentrated solutions of HCl acid is an important procedure, performed to increase production and to remove formation damage. Because the acid must be pumped through steel production tubing before entering the formation, it must contain corrosion inhibitors. These inhibitors must function for at least 2 hours while the acid is being pumped into the produci...

The kinetic consequences of resonance tunnelling processes that may occur in chemical reactions are investigated in terms of a multi-centered unsymmetrical Eckart potential barrier. This potential function does not only simulate the possible existence of intermediate wells in the effective potential energy cut along the reaction path, but also is amenable to analytic solutions. The reaction rate as well as its dependence on temperature, reduced mass,Q-value, activation energy and barrier diffuseness are evaluated for successively increasing the number of barrier stages. Comparisons between results due to single and multi-humped potential energy barriers are made and discussed.

The reaction of an equimolar mixture of H2 and CO was studied over ZrOr at 350 to 45O"C, 35 atm total pressure, and varying residence times. The isosynthesis reaction mechanisms were studied by monitoring the incorporation of oxygenated compounds into the isosynthesis products. Propionaldehyde and [t3C]acetone, [i3C]isopropanol, and [W]methanol were added to the CO/Hz reactant stream. Their effect on the isosynthesis product distributions and on the isotopic distribution of the products was monitored as a function of oxygenate feed rate. Propionaldehyde, acetone, and methanol were found to incorporate into the isosynthesis products. The isotopic distribution of the products was used to support an isosynthesis reaction scheme that involves CO insertion into a bound aldehyde or ketone as the major chain growth step and a second chain growth step that involves condensation between methoxide and a surface bound enolate. Q 1988 Academic press, IK.

Silica-alumina in the form of diethylamine (deam)-, dimethylamine (dmam)-, ethylamine (earn)-, ammonia (amm)-and aniline (an)-copper (II) complexes as well as deam-cobalt (II) complex have been used as potentially active catalysts for HzOz decomposition in an aqueous medium. The reaction was first order with respect to the H202 concentration and the rate constants (per g of dry silica-alumina) were determined. A coloured compound, a peroxo-metal complex, which formed at the beginning of the reaction in each case, was found to contain the catalytically active species. The activation energy and the change in the entropy of activation increased with the basicity of the ligands in the following order: an < amm < earn < dmam < deam, which is also the probability sequence for the formation of the activated complex. A reaction mechanism was proposed.

We show that a liquid mixture in the thermodynamically stable homogeneous phase can undergo a phaseseparation transition when rotated at sufficiently high frequency ω. This phase-transition is different from the usual case where two liquids are immiscible or where the slow sedimentation process of one component (e.g. a polymer) is accelerated due to centrifugation. For a binary mixture, the main coupling is due to a term ∝ ∆ρ(ωr) 2 , where ∆ρ is the difference between the two liquid densities and r the distance from the rotation axis. Below the critical temperature there is a critical rotation frequency ωc, below which smooth density gradients occur. When ω > ωc, we find a sharp interface between the low density liquid close to the center of the centrifuge and a high density liquid far from the center. These findings may be relevant to various separation processes and to the control of chemical reactions, in particular their kinetics. Séparation de phases des liquides miscibles dans une centrifugeuse Résumé Nous prouvons qu'un mélange de liquides dans une phase homogène thermodynamiquement stable peut subir une transition de phase une fois centrifugéá une fréquence ω suffisammentélevée. Cette transition de phase est différente du cas habituel où deux liquides sont non-miscibles ou du cas où un processus lent de sédimentation d'un composant (par exemple un polymère) est accéléré par une centrifugation. Pour un mélange binaire, le couplage principal est dûà un terme ∝ ∆ρ(ωr) 2 , où ∆ρ est la différence des densités entre les deux liquides et r est la distance de l'axe de rotation. Au-dessous de la température critique, il y a une rotation critique de fréquence ωc ; au-dessous d'ωc, de faibles gradients de densité prennent naissance. Quand ω > ωc, nous trouvons une interface mince entre le liquide de faible densité près du centre de la centrifugeuse et un liquideà haute densité loin du centre. Ces résultats peuventêtre appropriésà divers processus de séparation et au contrôle de réactions chimiques, en particulier de leur cinétique.

Catalytic transfer hydrogenation of soybean lecithin has been studied using aqueous sodium formate solution as hydrogen donor and palladium on carbon as catalyst. Kinetic constants and selectivity have been determined at intensive stirring. Hydrogenation reactions followed the first-order kinetics with respect to fatty acids. In addition to short reaction time, this method offers safe and easy handling. Hydrogenated soybean lecithin provides products with increased stability with respect to oxidation, mostly applied in cosmetics and pharmaceutical preparations.

1] Persistent meteor trains, studied for more than a century, remain somewhat mysterious [Newton, 1869;. The Leonids meteor showers of recent years afforded opportunities to apply new research technologies, including lidars and sophisticated cameras. Here we explore a particularly curious but common feature: double trains. Since the traditional hollow cylinder explanation has been shown to be untenable, we suggest a new explanation, arguing that one train is due to gaseous vapor train emissions behind the meteor while the other is due to heterogeneous chemistry associated with recoagulated dust. In this model the separation is caused by gravitational sedimentation of dust particles, an idea supported by rocket-based observations of recoagulated dust behind a meteor, by rocket-based observations of enhanced sodium emissions in a dust layer, by rocket observations of a dusty trail, and by recent theoretical estimates of chemical reactions on dust.

We study the liquid structure and solvation forces of dense monovalent electrolytes (LiCl, NaCl, CsCl, and NaI) in a nanometer slab-confinement by explicit-water molecular dynamics (MD) simulations, implicit-water Monte Carlo (MC) simulations, and modified Poisson-Boltzmann (PB) theories. In order to consistently coarse-grain and to account for specific hydration effects in the implicit methods, realistic ion-ion and ion-surface pair potentials have been derived from infinite-dilution MD simulations. The electrolyte structure calculated from MC simulations is in good agreement with the corresponding MD simulations, thereby validating the coarse-graining approach. The agreement improves if a realistic, MD-derived dielectric constant is employed, which partially corrects for (water-mediated) many-body effects. Further analysis of the ionic structure and solvation pressure demonstrates that nonlocal extensions to PB (NPB) perform well for a wide parameter range when compared to MC simulations, whereas all local extensions mostly fail. A Barker-Henderson mapping of the ions onto a charged, asymmetric, and nonadditive binary hard-sphere mixture shows that the strength of structural correlations is strongly related to the magnitude and sign of the salt-specific nonadditivity. Furthermore, a grand canonical NPB analysis shows that the Donnan effect is dominated by steric correlations, whereas solvation forces and overcharging effects are mainly governed by ion-surface interactions. However, steric corrections to solvation forces are strongly repulsive for high concentrations and low surface charges, while overcharging can also be triggered by steric interactions in strongly correlated systems. Generally, we find that ion-surface and ion-ion correlations are strongly coupled and that coarse-grained methods should include both, the latter nonlocally and nonadditive (as given by our specific ionic diameters), when studying electrolytes in highly inhomogeneous situations.

The asymptotic structure of laminar, moderately rich, premixed methane flames is analyzed using a reduced chemical-kinetic mechanism comprising four global reactions. This reduced mechanism is different from those employed in previous asymptotic analyses of stoichiometric and lean flames, because a steady-state approximation is not introduced for CH 3 . The aim of the present analysis is to develop an asymptotic model for rich flames, which can predict the rapid decrease of the burning velocity with increasing equivalence ratio . In the analysis, the flame structure is presumed to consist of three zones: a preheat zone with a normalized thickness of the order of unity, a thin reaction zone, and a postflame zone. The preheat zone is presumed to be chemically inert, and in the postflame zone the products are in chemical equilibrium and the temperature is equal to the adiabatic flame temperature T b . In the reaction zone the chemical reactions are presumed to take place in two layers: the inner layer and the oxidation layer. The rate constants of these reactions are evaluated at T 0 , which is the characteristic temperature at the inner layer. In the inner layer the dominant reactions taking place are those between the fuel and radicals, and between CH 3 and the radicals. An important difference between the structure of the inner layer of rich flames and that of lean flames analyzed previously is the enhanced influence of the chain-breaking reaction CH 3 ϩ H ϩ (M) 3 CH 4 ϩ (M) in rich flames. Here M represents any third body. This reaction decreases the concentration of H radicals, which in turn decreases the values of the burning velocity. In the oxidation layer of rich flames, the reactive-diffusive balance of O 2 is considered. This differs from the structure of the oxidation layer of lean flames where the reactive-diffusive balance of H 2 and CO was of primary interest. The burning velocities calculated using the results of the asymptotic analysis agree reasonably well with the burning velocities calculated numerically using chemical-kinetic mechanisms made up of elementary reactions. The values of the characteristic temperature at the inner layer T 0 are found to increase with increasing values of the equivalence ratio and to approach T b at ϭ 1.36. When T 0 is very close to T b , the asymptotic analysis developed here is no longer valid and an alternative asymptotic analysis must be developed for even larger equivalence ratios.

t h e a/x* frontier molecular orbital interaction (vs. ./a*) leads to a [2 + 21 cycloaddition reaction (nonconcerted) product. Theoretical calculations" support this conclusion. Experimental Section Melting points were obtained on a Mel-Temp apparatus and are uncorrected. Infrared spectra were obtained on a Perkin-Elmer Model 467 spectrometer. Field desorption mass spectra were obtained on a Finnigan MAT 31 1A mass spectrometer. All IH NMR spectra were obtained on a Bruker WH-200 instrument, and the chemical shifts are reported in ppm from internal TMS. The proton-decoupled ,'P spectra were acquired on a Bruker HX90E/SXP spectrometer using the standard multinuclear probe head. Samples were run with CDCI, as solvent in 10-mm tubes. Chemical shifts were measured relative to an external capillary of 85% aqueous H,PO,. Typical conditions: recycle time, 10 s; 90' rf pulse width, 15 f i s ; spectral width, 12048 Hz in 8192 points. Crystals suitable for the X-ray structure were made by recrystallizing 3 from chloroform. The X-ray intensity data (1 1369 reflections, 2.0° 5 28 5 50.0°, h,=tk,=tl, 28 scan) from a single crystal of 3 were recorded on a Syntex P2 four-circle diffractometer at ambient temperature using graphite-monochromated Mo K a radiation. The 2780 reflections with I > 3.0a(I) were corrected for Lorentz, decay, and polarization effects. The initial P and 0 atom positions were located with MULTAK. All (12) Bancroft, B., private communication, Mar 1986. remaining non-hydrogen atom positions were located by subsequent difference Fourier techniques. All copputations were made with the UCLA Crystallographic Package installed on a DEC VAX 8600/750 cluster. Preparation of 3. la (10 g, 12.5 mmol) is sublimed at 220 OC (1-1.2 kPa) for 4 h. The sublimate (-6 g) is then stirred in diethyl ether (25-30 mL) for 20 min to extract la. Filtration affords 3.2 g (32%) of nearly pure3 product: mp 174-182 OC; IR (Nujol)

This review highlights the many roles mass spectrometry plays in the discovery and development of new therapeutics by both the pharmaceutical and the biotechnology industries. Innovations in mass spectrometer source design, improvements to mass accuracy, and implementation of computer-controlled automation have accelerated the purification and characterization of compounds derived from combinatorial libraries, as well as the throughput of pharmacokinetics studies. The use of accelerator mass spectrometry, chemical reaction interface-mass spectrometry and continuous flow-isotope ratio mass spectrometry are promising alternatives for conducting mass balance studies in man. To meet the technical challenges of proteomics, discovery groups in biotechnology companies have led the way to development of instruments with greater sensitivity and mass accuracy (e.g., MALDI-TOF, ESI-Q-TOF, Ion Trap), the miniaturization of separation techniques and ion sources (e.g., capillary HPLC and nanospray), and the utilization of bioinformatics. Affinity-based methods coupled to mass spectrometry are allowing rapid and selective identification of both synthetic and biological molecules. With decreasing instrument cost and size and increasing reliability, mass spectrometers are penetrating both the manufacturing and the quality control arenas. The next generation of technologies to simplify the investigation of the complex fate of novel pharmaceutical entities in vitro and in vivo will be chip-based approaches coupled with mass spectrometry.

Because of great importance of thermal instability in nature, chemical processes, separation processes, and industrial applications as well as in geophysical and astrophysical engineering, the effect of thermal diffusion on unsteady MHD free convective heat and mass transfer flow past an inclined surface with heat generation has been investigated in this paper. Numerical as well as differential perturbations of solutions for the primary velocity field, secondary velocity field, temperature distribution as well as concentration distributions are obtained for associated parameters using the explicit finite difference method. The obtained results are discussed with the help of graphs to observe effects of various parameters on the above mentioned quantities. Finally, important findings of the investigations are concluded.

In this paper, a comprehensive computational fluid dynamics (CFD) modelling study was undertaken by integrating the combustion of pulverized dry lignite in several combustion environments. Four different cases were investigated: an air-fired and three different oxy-fuel combustion environments (25 vol.% O 2 concentration (OF25), 27 vol.% O 2 concentration (OF27), and 29 vol.% O 2 concentration (OF29) were considered. The chemical reactions (devolatilization and char burnout), convective and radiative heat transfer, fluid and particle flow fields (homogenous and heterogenous processes), and turbulent models were employed in 3-D hybrid unstructured grid CFD simulations. The available experimental results from a lab-scale 100 KW firing lignite unit (Chalmer's furnace) were selected for the validation of these simulations. The aerodynamic effect of primary and secondary registers of the burner was included through swirl at the burner inlet in order to achieve the flame stability inside the furnace. Validation and comparison of all the combustion cases with the experimental data were made by using the temperature distribution profiles and species concentration (O 2 , CO 2 , and H 2 O) profiles at the most intense combustion locations of the furnace. The overall visualization of the flame temperature distributions and oxygen concentrations were presented in the upper part of the furnace. The numerical results showed that the flame temperature distributions and O 2 consumptions of the OF25 case were approximately similar to the reference combustion case. In contrast, in the OF27 and OF29 combustion cases, the flame temperatures were higher and more confined in the closest region of the burner exit plane. This was a result of the quick consumption of oxygen that led to improve the ignition conditions in the latter combustion cases. Therefore, it is concluded that the resident time, stoichiometry, and recycled flue gas rates are relevant parameters to optimize the design of oxy-fuel furnaces. The findings showed reasonable agreement with the qualitative and quantitative measurements of temperature distribution profiles and species concentration profiles at the most intense combustion locations inside the furnace. These numerical results can provide useful information towards future modelling of the behaviour of pulverized brown coal in a large-scale oxy-fuel furnace/boiler in order to optimize the burner's and combustor's design.

Many different circuit models have been proposed for double-layer capacitors (DLCs). Presented in this paper is an evaluation of the Debye polarization cell as a model for a double-layer capacitor (DLC). In comparison to other circuit models, the primary advantage of this model is that the circuit elements can be related to chemical reactions which occur inside the DLC. The circuit element values are found from ac impedance measurements for a DLC and a computer program which utilizes a nonlinear least-squares fitting technique. Variations in circuit element values with dc bias level and manufacturing have been investigated. The performance of the Debye polarization cell in slow discharge and pulse load applications has been compared to actual circuit measurements and to simulated results using a classical equivalent circuit.

' C02, ethane, and fluoroform. While these fluids interact similarly with nonpolar solutes, they exhibit markedly different hydrogen bonding characteristics, as demonstrated by their influence on the tautomeric equilibria between the azo (hydrogen bond donor) and hydrazone (hydrogen bond acceptor) forms of 4-phenylazo-1 -naphthol. Recently, , utilized photophysical techniques to probe local density augmentation in supercritical fluids, but hydrogen bonding was not considered. Another interesting example of hydrogen bonding is the pronounced enhancement in the solubilities of certain solutes in a supercritical fluid with the addition of a cosolvent, for example, ethanol or tributyl phosphate . Even greater solubility enhancement has been observed in organized molecular assemblies composed of surfactants. Randolph et al.