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MODEL PREDICTS PROMISING HEA ALLOYS Researchers at Texas A&M University, College Station, working with colleagues at the DOE's Ames National Laboratory, Iowa, developed an artificial intelligence (AI) framework capable of [...]

Polystyrene-grafted attapulgite (ATP-g-PS) was prepared using surface-initiated redox initiation via graft from approach. ATP was modified with (3-aminopropyl) triethoxysilane (APTES) to anchor amine on the surface (ATP-N[H.sub.2]), and then ATP-N[H.sub.2] was further treated with 4-(diethylamino) salicylaldehyde (DEAS) to give aromatic tertiary amine groups functional ATP (ATP-ATA). Subsequently, the surface-initiated redox polymerization of styrene in the presence of ATP-ATA and benzoyl peroxide (BPO) was performed to afford ATP-g-PS. The chemical grafting of PS on the surface of ATP was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The crystal structure of PS-grafted ATP was characterized by X-ray diffraction (XRD) analysis. The morphology of ATP-g-PS was observed by scanning electron microscopy (SEM). POLYM. ENG. SCI., 55:889-895, 2015. [C] 2014 Society of Plastics Engineers, INTRODUCTION Nowadays, inorganic nanoparticles are widely used in polymer to endow the multiphase system excellent properties by utilizing mechanical, biochemical, and thermal characteristics of inorganic nanoparticles [1-4]. The exceptional properties [...]

The paper presents the results of studying the composition of low-molecular products of the thermal oxidative destruction of atactic polypropylene by gas chromatography/mass spectrometry. Special attention has been paid to the investigation of the mass spectra of compounds dominating in the composition of low-molecular products of the incomplete oxidative destruction of the original polymer, carried out for the synthesis of components for composite materials of the new generation. The most probable molecular structures of the studied compounds are determined on the basis of fragmentation patterns. Keywords: gas chromatography/mass spectrometry, selective ion detection, thermal oxidative destruction, products of polypropylene oxidation, atactic polypropylene DOI: 10.1134/S1061934812130047, INTRODUCTION Nowadays plastics present the most wide-spread class of materials. The possibility of regulating their physicochemical properties in a wide range by even negligible changes in their composition or by [...]

Reactor experiments were conducted to study aerobic sulfide oxidation in pulp and paper wastewaters under typical operating conditions. Data produced from these experiments were used to develop a set of sequential rate equations that describe the significant sulfide and oxygen processes in the reactors. Model parameters were estimated for three different pulp and paper wastewaters using a multiresponse procedure. The sulfide oxidation rate coefficients for the wastewaters ranged from 0.108 to 0.155 [min.sup.-1] at 35[degrees]C and approximately neutral pH. The reaction order with respect to oxygen could not be precisely estimated but appeared to be near the lower boundary for the fitting procedure (essentially zero order). Modeling of the oxygen depletion data provided evidence that the first sulfide oxidation reaction product consumed 0.5 mg of oxygen per mg of sulfide oxidized, suggesting polysulfides and elemental sulfur as the initial reaction products. The oxygen depletion modeling also suggested oxidation of the initial reaction product to a more stable intermediate which is postulated to be thiosulfate. DOI: 10.1061/(ASCE)EE.1943-7870.0000248 CE Database subject headings: Models; Hydrogen sulfides; Estimation; Paper mills; Waste stabilization ponds; Oxidation. Author keywords: Models; Hydrogen sulfides; Estimation; Paper mills; Waste stabilization ponds.

Analytical expressions for the current--potential and charge-potential curves of an electrocatalytic process taking place at redox mediator modified electrodes corresponding to the application of cyclic staircase or cyclic sweep potentials are presented. Simple equations for cyclic voltsmmetry and cyclic volteoulometry curves have been also deduced for the usual experimental case corresponding to high catalytic rate constants, showing that whereas the current reach an stationary behavior, the charge always depend on time. The value of the rate constant of the chemical step can be easily determined from the plateau of the voltammogram or from the linear anodic region of the charge potendal curves. The theoretical predictions have been tested with the electeocatalytic oxidation of ascorbate mediated by a mixed 6-(ferroeenyl)hexanethiol-butanethiol monolayer at a disk gold electrode, with an excellent agreement between theory and experiments. A catalytic rate constant 3440 [M.sup.-1] [s.sup.-1] has been obtained, which is higher than those previously reported for this system with longer alkanethiol chains.

A functional heme/nonheme nitric oxide reductase (NOR) model is presented. The fully reduced diiron compound reacts with two equivalents of NO leading to the formation of one equivalent of [N.sub.2]O and the bis-ferric product. NO binds to both heme Fe and nonheme Fe complexes forming individual ferrous nitrosyl species. The mixed-valence species with an oxidized heme and a reduced nonheme [Fe.sub.B] does not show NO reduction activity. These results are consistent with a so-called 'trans' mechanism for the reduction of NO by bacterial NOR. functional model | NO reduction | [N.sub.2]O | 'trans' mechanism

In recent years the application of partial nitrification techniques has been denoted as very promising. These methods arc based on the oxidation of ammonia to nitrite and the inhibition of the nitratation using different strategies. In most cases, this inhibition causes an increase in the concentration of nitrite. However, the effect of high nitrite concentrations under low dissolved oxygen (DO) conditions on the nitrification process is not well understood. In this paper, the effect of ammonia, nitrite, and nitrate concentrations on the nitrification process under low dissolved oxygen concentrations were studied using respirometric techniques. Results showed that the specific oxygen uptake rate (SOUR) followed a Monod-type equation with respect to the DO concentration. The coefficient SOU[R.sub.m] was constant with respect to the ammonia, nitrite, and nitrate within the tested concentrations; in addition, [K.sub.O] was constant with respect to ammonia and nitrate but it increased linearly with the nitrite concentration, suggesting that nitrite was a competitive inhibitor of the SOUR. The inhibitory effect of nitrite was reverted by washing, in accordance with a competition model. From the data obtained using the open respirometer, the ratio between the oxygen consumption (OC) corresponding to each pulse of ammonia at different nitrite concentrations and the OC in the absence of nitrite (O[C.sub.O]) was calculated. The experimental ratio OC/O[C.sub.O]) was almost constant with respect to the nitrite concentration and it was close to the literature value. Finally, simulation results agree with the experimental data confirming that the proposed competition model represented adequately the inhibitory effect of nitrite on the respiration rate of ammonia-oxidizing bacteria. DOI: 10.1061/(ASCE)0733-9372(2008)134:3(184) CE Database subject headings: Nitrification; Ammonia; Nitrates; Biological treatment; Bacteria; Simulation.

We have developed dynamic tumor vascular phantoms and utilized them to investigate the biphasic behavior of increases in light absorption, which is directly associated with oxygenated hemoglobin concentration that was observed in vivo from rat breast tumor experiments during carbogen/oxygen inhalation. The experimental setup for the phantom study included a continuous-wave, multichannel, near-infrared spectroscopy (NIRS) system and syringe pumps to drive the simulated blood through the dynamic vascular phantoms. The results from such phantom experiments clearly show that the two time constants observed in tumor oxygenation dynamics in vivo can result from two different perfusion rates or two different blood flow velocities. We provide experimental support for our previous hypothesis: the biphasic tumor hemodynamic feature stems from a well-perfused and poorly perfused region that could be detected with the two time constants of the NIRS signals. With a multichannel approach, noninvasive NIRS measurements may have useful and prognostic values to quantify the therapeutic effects of cancer treatments. OCIS codes: 170.1470, 170.3660, 170.4580, 170.5280, 170.6510, 290.1990.

A detailed chemistry-based CFD model was developed to simulate the diesel spray combustion and emission process. A reaction mechanism of n-heptane is coupled with a reduced N[O.sub.x] mechanism to simulate diesel fuel oxidation and N[O.sub.x] formation. The soot emission process is simulated by a phenomenological soot model that uses a competing formation and oxidation rate formulation. The model is applied to predict the diesel spray lift-off length and its sooting tendency under high temperature and pressure conditions with good agreement with experiments of Sandia. Various nozzle diameters and chamber conditions were investigated. The model successfully predicts that the sooting tendency is reduced as the nozzle diameter is reduced and/or the initial chamber gas temperature is decreased, as observed by the experiments. The model is also applied to simulate diesel engine combustion under premixed charge compression ignition (PCCI) conditions. Trends of heat release rate, N[O.sub.x], and soot emissions with respect to EGR levels and start-of-injection timings are also well predicted. Both experiments and models reveal that soot emissions peak when the start of injection (SOI) occurs close to TDC. The model indicates that low soot emission at early SOI is due to better oxidation while low soot emission at late SOI is due to less formation. Since N[O.sub.x] emissions decrease monotonically with injection retardation, a late injection scheme can be utilized for simultaneous soot and N[O.sub.x] reduction for the engine conditions investigated in this study. [DOI: 10.1115/1.2181596]

The validity of chemiluminescence-based methods relies upon the uniqueness of the relationship between the concentration of the analyte and the intensity of chemiluminescence produced. We have examined the chemiluminescence of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) in the presence of [O.sub.2], without added [H.sub.2][O.sub.2], to measure nanomolar concentrations of total Fe(II) (both inorganically and organically complexed) in aqueous samples. To test the validity of the method, we have developed a kinetic model that describes the two-step oxidation of luminol by superoxide and hydroxyl (or hydroxyl-like) radicals produced from the oxidation of Fe-(II) by [O.sub.2] by synthesis of existing published data. This model was coupled with a model for Fe(II) oxidation by [O.sub.2] in the presence and absence of the naturally occurring Suwannee River fulvic acid (SRFA). The production of chemiluminescence depended upon the concentrations of free radicals in both the sample and luminol reagent and the pH at which the reactions were performed. The relationship between Fe(II) concentration and chemiluminescence intensity was found to be unique at Fe(II) concentrations from 1 nM to 1 [micro]M without organic complexation and from 1 to 32 nM in the presence of SRFA despite strong signal quenching in the latter case. This type of behavior will likely ensure a similarly unique relationship in the presence of a wide range of organic compounds; however, when other systems are being investigated, the technique should be carefully evaluated.

Analysis of the manganese-cluster, containing photosystem II, reveal that the electron pathway to P680(sup)+ in the oxygen-evolving system appears to follow a branched pathway instead of linear or parallel pathway. Structural data support the branched model.

Characteristics of Black Sea water are presented, focusing on oxygen, nitrate, hydrogen sulfide, manganese and ammonium contents. Dissolved oxygen is reduced to trace levels above the nitrate reduction zone; hydrogen sulfide increases within the anoxic pool's deeper levels, where nitrate is no longer detectable; and ammonium and manganese concentrations increase below the suboxic layer.

Byline: H.S. Sidhu (1), M.I. Nelson (1), G.N. Mercer (1), R.O. Weber (1) Keywords: exothermic reaction; bifurcation; flammability limits; flow reactor Abstract: This paper investigates the bifurcation behaviour of a model oxidation reaction in a continuously stirred tank reactor (CSTR). We assume that two gaseous chemical species are pumped separately into the CSTR, at constant total pressure, reacting to produce an inert product. The reaction is assumed to be a single step reaction that is described by Arrhenius kinetics. It is capable of producing oscillatory behaviour as well as steady state multiplicity in certain parameter regions. Bifurcation diagrams in various control parameter spaces are presented. We show that the system always possesses a globally attracting invariant region. The equivalence of a CSTR having n feed streams and the one pipe version, by appropriate rescaling, is also discussed. Author Affiliation: (1) School of Mathematics and Statistics, University College, University of New South Wales, Australian Defence Force Academy, Canberra, 2600, Australia Article History: Registration Date: 08/10/2004

Research examines transfer of hydrides between pyridine nucleotide coenzymes and a redox substrate and the stereochemistry of the redox reactions. Data are presented for the reaction mechanisms in terms of stereoslectivity preferences, the isotope effect, and the reaction kinetics.

A computational simulation of the oxidation of chemical species inside a metal emitter electrospray ion source, in the context of electrospray mass spectrometry (ES-MS), has been developed. The analysis code employs a boundary integral method for the solution of the Laplace equation for the electric potential and current and incorporates standard activation and concentration polarization functions for the redox-active species in the system to define the boundary conditions. This paper provides a demonstration of the capability of this simulation method. Due to the approximate nature of some of the input data, and certain simplifying assumptions, the present results must be considered semiquantitative. The specific system modeled consisted of a 100-(mu)m-i.d., inert metal capillary ES emitter and a spray solution composed of an analyte dissolved in CH(sub 3)CN/H(sub 2)O (90/10 v/v). Variable parameters included the concentration (i.e., 5.0, 10, 20, and 50 (mu)M) of the easily oxidized analyte ferrocene (Fc, dicyclopentadienyl iron) in the solution, and solution conductivities of 1.9, 3.8, and 7.6 x 10(super -7) (omega)(super -l)/cm, with an operational flow rate of 5.0 (mu)L/min and ES currents on the order of 0.05 (mu)A. Under these defined conditions, the two most prominent reactions at the emitter metal/solution interface were assumed to be H(sub 2)O oxidation (2H(sub 2)O = O(sub 2) + 4H(super +) + 4e(super -)) and ferrocene oxidation (Fc = Fc(super +) + e(super -)). Using this model, it was possible to predict the interfacial potentials, as well as the current density for each of the reactions, as a function of axial position from the emitter spray tip back upstream, under the various operational conditions. The simulations show that the majority of the current from the redox reactions is generated within a 200-300-(mu)m region near the spray tip. The lower the value of E(super 0) for a specific reaction, the further upstream from the tip the reaction extends.

A comparison of the heterogeneous electron-transfer rate constants of both flexible and rigid series of redox-active, iron-sulfur core dendrimers is presented. The flexible series were less effective at attenuating the rate of electron transfer than the rigid series.

Manganese (Mn) in a drinking water distribution system can cause multiple aesthetic problems including discolored water and fouling or scaling of fixtures. Oxidation and solid-liquid separation processes are typically employed at a treatment plant to limit the concentration of Mn entering the distribution system. Potassium permanganate (KMn[O.sub.4]) is commonly used to oxidize the manganous ion ([Mn.sup.+2]) to manganese oxide (Mn[O.sub.2]). In this study, a mechanistic model is applied to the oxidation of manganese at a treatment plant. Literature kinetic constants (determined with artificial water) are compared with the values obtained for the plant's natural water. The solution and surface phase oxidation rate constants determined with the natural water are two to six orders of magnitude less than those determined with the artificial water. The reduced oxidation rate in the natural water is attributed to the presence of dissolved organic matter, which can exert a competitive demand on the oxidant and interfere with the oxidation by complexing [Mn.sup.+2]. The development of an additional rate constant for the oxidation of dissolved organic matter improves the modeling results for KMn[O.sub.4] concentration versus time, but only marginally explains the [Mn.sup.+2] oxidation rate differences.

A model based on Monod kinetics and originally developed for use with rotating biological contactors was modified for use with a packed-bed column reactor. The reactor was filled with expanded polystyrene beads to immobilize chemolithotrophic bacteria and fed up to 570 mg [L.sup.-1] ([approximately]10 mM) ferrous iron [Fe(II)] in simulated acid mine drainage. A tracer study indicated changing behavior as a function of hydraulic residence time (HRT), with a transition from complete mix flow behavior to plug flow behavior as HRT decreased. The Fe(II) oxidation efficiency exceeded 95% until the HRT was reduced below 0.5 h. The reactor performance could be predicted with the model using estimates from the literature for [Mathematical Expression Omitted] and Y. The experimentally determined half-saturation constant [K.sub.s] was found to range from 5 to 12 mg [L.sup.-1]. The maximum volumetric capacity constant [R.sub.max] was estimated to be [approximately]360 mg Fe(II)[h.sup.-1] [L.sup.-1] beads under complete mix flow conditions but appeared to be as high as 724 mg Fe(II)[h.sup.-1] [L.sup.-1] beads as conditions approached plug flow at short HRTs.

A simple model for the design of selective catalytic reduction (SCR) process is presented. The two-dimensional mass transfer equation shown in Bai and Chwu (1997) is simplified and the analytic solution is obtained. The analytic solution is verified by the solution of the numerical two-dimensional model as well as published experimental data. Then it is applied for the design of the SCR reactor. Effects of operating temperature, inlet molar ratio of [NH.sub.3]/NO, channel pitch, and gas flow rate on the SCR reactor volume are evaluated based on a designed NO removal efficiency. The [NH.sub.3] slip problem of a given inlet ratio of [NH.sub.3]/NO also is discussed. It is shown that the injection ratio of [NH.sub.3]/NO must be slightly higher than the desired NO removal efficiency so that the reactor volume can be reduced and the problem of [NH.sub.3] slip is not a major concern.

A model for iron oxidation and speciation by molecular oxygen, incorporating the specific interaction theory of Pitzer, was utilized to determine ferrous iron speciation in different aquatic environments. Results showed natural waters with more than 1 millimole of carbonate alkalinity to be replete with ferrous carbonate complexes. The constructed model proved to be adept at forecasting oxidation levels in aquatic systems such as seawater, lake water, and salt solutions.

A study relating to research on electron transfer reactions in ionic microheterogenous media was conducted to develop a system to derive electron transfer quenching rate constants at the micellar surface without the need for the application of complex equations typical in such experiments. The system uses the Stern-Volmer treatment to determine quenching rate constants since the donor does not associate with sodium dodecyl sulfate micelles and the acceptor remains bound to the micelle during the lifetime of the probe.

A study relating to research on synthetic reaction center models was conducted to synthesize and investigate a rigidly linked porphyrin-quinone dyad. It was found through cyclic voltammetry that although the structural relationship, ground-state absorption properties and electrochemical properties of this dyad is very close to those of another, synthesized porphyrin-quinone dyad, their photoinduced electron-transfer attributes are markedly different.

Research was undertaken to determine the interaction between fluid fluxes, fluid compositions and mass transfer during medium crustal metamorphic conditions through the development of one-dimensional numerical models of coupled porous media flow and oxidation-reduction reactions. The redox state has a basic control on mineral assemblages, mineral composition and fluid compositions evolving during crustal metamorphism. Results revealed that reaction times primarily influenced spatial and temporal patterns of mineralogic evolution.

The purpose of this paper is to propose certain dynamical principles in biological systems, which can be used to explain the effectiveness of charge transfer or excitation transfer in biological systems. Some of these systems are accessible experimentally.

A mathematical model of oxidation of SixGe1-x alloys has been developed. Numerical methods were employed to simulate the growth of SiO2 and to determine silicon distribution in the alloys. The model is based on the assumption of simultaneous oxidation of germanium and silicon when the SixGe1-x is exposed to an oxidizing atmosphere. The results indicate that the model is capable of characterizing the oxidation process.

Thioglycolic acid (h2tga) and beta-PhNHOH substrates, which simultaneously act as electron and proton donors, are used to research the reactivity of the Mo-Ot bonds of a tridentate anionic sulfur (ONS) ligand's cis-dioxomolybdenum(VI) complex. An oxo-transfer path is followed in the H2tga reaction via a coupled proton-electron transfer mechanism. The spectator oxo effect stabilizes the three-membered metallacycle ring contained within a seven-coordinate species in the beta-PhNHOH product.

The two-term rate law -d(C1O(sub 2))/dt = k(subI)(C10(sub 2))(I(super -)) + k(sub II)(C1O(sub 2))(I(super -))(super 2) can be confirmed for the reaction of iodide ion oxidation by chlorine dioxide. Stopped-flow techniques at I = 1.0 M (NaC1O4) were used to study the oxidation. An outer-sphere electron-transfer mechanism is used to interpret the third-order and second-order paths.

Models for the kinetic analysis of intermolecular protein electron transfer (ET) reactions in the physiologic temperature range are presented. The models interpret the effects of temperature on reaction rates, reorganization energy, and electronic coupling between donor and acceptor proteins based on two criteria: temperature-dependent changes in protein conformation, and correlation of the rate of reaction with ET distances predicted from protein crystal structures.

Simulation of the growth of phototrophic sulfur oxides under constant concentrations of hydrogen sulfide in the culture and under conditions of changing illumination was conducted to represent the redox of the culture. Variations in biological activity were associated with variations in redox potential, suggesting that changes in redox are caused by changes in the culture conditions.

The energetics and kinetics of the radical pair states in photosynthetic reaction centers from wild-type Rhodobacter sphaeroides during electron transfer processes were investigated by femtosecond experiments and a novel kinetic scheme. Kinetics data favored the reversible model over the pure forward model. An analysis of the results in terms of electron transfer theory is provided.

A study has been conducted to describe the synthesis and multistep electron transfer kinetics of zinc methylenechlorin-porphyrin-pyromellitimide triads, ZC-HP-I and ZC-ZP-I and their related dyads. Only the emission from ZC was observed by flourescence spectroscopy, suggesting that ZC contains an efficient intramolecular electron transfer strategy. The synthesis of model compounds with natural photosynthetic reaction centers is explained.

The chemical oxidation of hydrogen peroxide and ultraviolet light was investigated in a continuous-flow stirred tank reactor under various experimental conditions. The results were used as basis for developing a kinetic model of the process. The accuracy of the kinetic system was verified by testing the model in pure water and in synthetic solutions.

The reaction of trans-dioxorhenium complex with methyl trifluoromethanesulfonate produces high-valent, highly stable oxo-, methoxorhenium complexes. These complexes are identical to analogous oxo, hydroxo complexes of trans-dioxorhenium(V)tetrapyridyl species, which is a model system for interfacial two-electron, two proton transfer reaction sequences. High pH stabilizes the rhenium(IV) state for several complexes with respect to redox disproportionation.

Phthalate dioxygenase reductase (PDR) is a prototypical iron-sulfur flavoprotein (36 kilodaltons) that utilizes flavin mononucleotide (FMN) to mediate electron transfer from the two-electron donor, reduced nicotinamide adenine nucleotide (NADH), to the one-electron acceptor, [2Fe-2S]. The crystal structure of oxidized PDR from Pseudomonas cepacia has been analyzed at 2.0 angstrom resolution resolution; reduced PDR and pyridine nucleotide complexes have been analyzed at 2.7 angstrom resolution. NADH, FMN, and the [2Fe-2S] cluster, bound to distinct domains, are brought together near a central cleft in the molecule, with only 4.9 angstroms separating the flavin 8-methyl and a cysteine sulfur ligated to iron. The domains that bind FMN and [2Fe-2S) are packed so that the flavin ring and the plane of the [2Fe-2S] core are approximately perpendicular. The [2Fe-2S] group is bound by four cysteines in a site resembling that in plant ferredoxins, but its redox potential (- 174 millivolts at pH 7.0) is much higher than the potentials of plant ferredoxins. Structural and sequence similarities assign PDR to a distinct family of flavoprotein reductases, all related to ferredoxin [NADP.sup.+-] reductase., A change in the currency of reducing equivalents, in which a flavin prosthetic group accepts two electrons as hydride ion [(H.sup.-)] and donates one electron at a time to iron-sulfur [...]

A cytochrome c oxidase model that consists of a cobalt(II) porphyrin with a copper(I) triazacyclononane macrocycle fastened on the distal face and an imidazole covalently attached to the proximal face has been synthesized and characterized. Redox titrations with molecular oxygen ([O.sub.2]) and cobaltocene were carried out, and [O.sub.2] was found to bind irreversibly in a 1:1 ratio to the model compound. This [O.sub.2] adduct (a bridged peroxide) can be fully reduced to the deoxygenated form with four equivalents of cobaltocene. The model compound was adsorbed on an edge-plane graphite electrode, and rotating ring-disk voltammetry was used to monitor the electrocatalytic reduction of [O.sub.2]. Four-electron reduction of [O.sub.2] was observed at physiological pH., Oxidative phosphorylation, a process required by all respiring organisms, involves four-electron ([4e.sup.-]) reduction of [O.sub.2] to [H.sub.2]O by the cytochrome c oxidase enzyme family (1-4). The active site of cytochrome [...]

The most powerful oxidant found in nature is compound Q, an enzymatic intermediate that oxidizes methane. New spectroscopic data have resolved the long-running controversy about Q's chemical structure., Bacteria that consume methane gas (C[H.sub.4]) to produce methanol (C[H.sub.3]OH) using dioxygen ([O.sub.2]) must break two chemical bonds: the bond holding the two oxygen atoms together, and one of the [...]