On the Synergy Effect in MoO3–Fe2(MoO4)3 Catalysts for Methanol Oxidation to Formaldehyde

Methanol oxidation to formaldehyde was studied over a series of Fe–Mo–O catalysts with various Mo/Fe atomic ratio and the end compositions Fe₂O₃ and MoO₃. The activity data show that the specific activity passes through a maximum with increase of the Mo content and is the highest for Fe₂(MoO₄)₃. The selectivity to formaldehyde, on the other hand, increases with the Mo content in the catalyst. A synergy effect is observed in that a catalyst with the Mo/Fe ratio 2.2 is almost as active as Fe₂(MoO₄)₃ and as selective as MoO₃. Imaging of a MoO₃/Fe₂(MoO₄)₃ catalyst by SEM and TEM shows that the two phases form separate crystals, and HRTEM reveals the presence of an amorphous overlayer on the Fe₂(MoO₄)₃ crystals. EDS line-scan analysis in STEM mode demonstrates that the Mo/Fe ratio in the amorphous layer is ~2.1 in the fresh catalyst and ~1.7 in the aged catalyst. The enrichment of Mo at the catalyst surface is confirmed by XPS data. Raman spectra give evidence for the Mo in the amorphous material being in octahedral coordination, which is in contrast to the crystalline Fe₂(MoO₄)₃ bulk structure where Mo has tetrahedral coordination. X-ray diffraction (XRD) analysis gives no support for the formation of a defective molybdate bulk structure. The results presented give strong support for the Mo rich amorphous structure being observed on the Fe₂(MoO₄)₃ crystal surfaces being the active phase for methanol oxidation to formaldehyde.     

High temperature mechanical properities and creep crack initiation of DS CM186LC for nozzle guide vane

The second generation DS alloy, CM186LC is used in the as-cast and double aged condition which has creep-rupture properities equivalent to the first generation single crystal alloys CMSX-2 and CMSX-3. In production, cast vane components have to be subjected to a brazing treatment for joining into pairs. The effect of the brazing treatment and modified brazing treatment (heat treatment) on mechanical properities at high temperature was studied in accordance with microstructure. Brazing treatments gave no effect on tensile properities and creep failure mode of DS CM186LC, although a small decrease in stress-rupture life was observed. Creep failure was related to the solidified microstructure. Creep cracks began at the grain boundary normal to the applied stress, especially at the γ/γ’ eutectic phase on grain boundaries. Most of γ/γ’ eutectics which had solidified at the last stage of casting, had microporosity which became a crack initiation site during creep. MC carbide reaction with the matrix γ was observed in the creep failed specimens.     

Domain organization of the extracellular region of CD45

CD45 is a large, heavily glycosylated, transmembrane proteinphosphotyrosine phosphatase found on all nucleated cells ofhaematopoietic origin. In lymphocytes, the cytoplasmic phosphataseis necessary for efficient signalling through the antigen receptorbut in contrast little is known about the interactions of theextracellular region of the molecule. This consists of a mucin-likeregion, a novel cysteine-containing region and a region containingthree putative fibronectin type III domains. To confirm thisorganization and to identify parts potentially important forfunction, we have expressed fragments of the extracellular domainof rat CD45 as recombinant soluble proteins. Proteins correspondingto two, three and four domains of CD45 were expressed in secretedforms. Single domains and constructs for proteins with truncationsof the predicted domains were not expressed. This is consistentwith the proposed structural organization. Determination ofthe positions of the disulphide bonds in the N-terminal cysteine-containingregion and the first fibronectin type III domain identifiednovel disulphide bonds within the fibronectin type III domainand an unusual inter-domain disulphide linkage. Circular dichroismspectroscopy indicated that this region of rat CD45 has mainlyß-strand secondary structure and no -helical content.These studies support the proposed domain organization of CD45.     

Cotton growth and yield as influenced by different timing of late-season foliar nitrogen fertilization

Foliar fertilization to meet the nitrogen (N) requirement of the cotton crop during the latter fruiting stages is a production practice that is not well understood. The objective of this study was to investigate the benefits of late-season foliar-N fertilization on growth and yield of cotton in relation to soil-N level and timing based on weeks after first flower (WAFF) and nodes above white flower (NAWF). A 4-year field study was conducted with four foliar-N treatments consisting of a control with no foliar-N, and one, two, or three foliar-N sprays under different soil-N regimes. In 1990, the foliar-N treatments were based on WAFF sprayed during fifth, sixth and seventh WAFF. Foliar-N significantly increased nodes above white flower (NAWF) over the control with no significant differences among the three foliar-N treatments. A negative relationship (r2=0.98) existed between NAWF and days after planting (DAP). Foliar-N also significantly increased plant height, leaf number, leaf area, leaf dry weight, boll number, boll dry weight and yield. The same foliar-N treatments were applied on low and high soil-N regimes in 1991 and 1992, and in 1993 on four different soil-N regimes, 0, 55, 82, and 110 kg N ha-1 at NAWF = 7, 6 and 5. No significant difference was found in NAWF among the four foliar-N treatments within each soil-N level during 1991. Significant differences between the control and the three foliar-N sprays were found for leaf area, boll number, and boll dry weight. In 1992, the NAWF of control plants showed a similar response to the 1990 control plants. In contrast, the foliar-N sprayed plants extended the highest NAWF for an additional week, after which it steadily declined below 5. Foliar-N significantly increased yield in 1990, yield and yield components in 1991 and 1992, and yield in 1993. Neither WAFF nor NAWF appear to be good indicators for timing late-season foliar-N fertilization. The study clearly demonstrated, however, that late-season foliar-N fertilization is beneficial to cotton plants, although the precise timing of such N application is still unclear.     

Tolerance to Thiarubrines from Ambrosia chamissonis by the Rare Moth Lasionycta wyatti

The larvae of a rare noctuid moth, Lasionycta wyatti, were found to be associated with the stems and roots of Ambrosia chamissonis, a species found along sandy beaches in western North America. High-performance liquid chromatographic (HPLC) analyses of L. wyatti larvae and their frass revealed significant amounts of thiarubrines, secondary compounds characteristic of this host plant. Artificial diet studies showed that thiarubrines were well tolerated by these larvae. These same diets, however, were toxic to larvae of Manduca sexta and inhibited larval growth of Spodoptera litura. Even in the presence of simulated sunlight, artificial diets containing thiarubrines did not affect larvae of L. wyatti. However, dietary incorporation of thiophenes, natural UV-activated breakdown products of thiarubrines, was deleterious to larvae of L. wyatti.     

Analytic Convergence Rates and Parameterization Issues for the Gibbs Sampler Applied to State Space Models

In this paper we obtain a closed form expression for the convergence rate of the Gibbs sampler applied to the unobserved states of a first-order autoregression plus noise model. The rate is expressed in terms of the parameters of the model, which are regarded as fixed. For the case where the unconditional mean of the states is a parameter of interest we provide evidence that a 'centred' parameterization of a state space model is preferable for the performance of the Gibbs sampler. These two results provide guidance when the Gaussianity or linearity of the state space form is lost. We illustrate this by examining the performance of a Markov chain Monte Carlo sampler for the stochastic volatility model.     

Temperature and frequency dependence of dielectric loss of Ba(Mg1/3Ta2/3)O3 microwave ceramics

Ba(Mg_1/3Ta_2/3)O₃ ceramic possessing extremely high Q × f value of more than 300 THz at microwave frequency was developed in our previous study. It is of great interest to understand the mechanism of microwave absorption in such a practical material. In the present study we report on the temperature dependence of the dielectric loss in the Ba(Mg_1/3Ta_2/3)O₃. The mechanism of the microwave absorption is discussed using two phonons difference process. The samples were prepared by conventional solid state reaction and sintered at 1893 K in oxygen atmosphere. Dielectric properties in the microwave range were measured by Hakki & Colemann and resonant cavity methods in the temperature range of 20–300 K. Whispering gallery mode technique was used for the measurement of the dielectric properties at the millimeter wave frequency. Dielectric loss of the Ba(Mg_1/3Ta_2/3)O₃ at the microwave frequency increases with temperature between 200 and 300 K in general agreement with the theory of intrinsic dielectric loss derived from the two phonon difference process. However below 200 K, the dielectric loss has shown a distinctive behavior with a loss peak at 40 K. It was inferred that the loss peak of the Ba(Mg_1/3Ta_2/3)O₃ was caused by the local orientation polarization having dispersion at the microwave frequency.     

Synthesis,characterization, and thermal behaviors of tannin stearates prepared from quebracho and pine bark extracts

Reported is the preparation of various condensed tannin stearates and the associated chemical characterization and thermal properties of these products. Stearate esters of condensed tannins from both quebracho and pine bark extracts were prepared in generally high, isolated yields from reaction with stearic acid chloride. Tannin esterification was confirmed by both Fourier transform infrared and nuclear magnetic resonance (NMR), and the average degree of stearate substitution was calculated from ¹H‐NMR analysis. Product degree of substitution (DS) was observed to proportionately increase with higher stearic acid chloride ratio with maximum DS values of 4.0 and 5.1 achieved for quebracho and pine tannins, respectively. Thermal analysis revealed that tannin stearate products have increased thermal stability with a degradation onset at significantly higher temperature for those samples possessing relatively greater DS. Analysis using differential scanning calorimetry revealed isolated products to consist of multiple components which exhibit interesting melt behaviors, a likely result from their work up on isolation. However, multiple melt features of the individual components in products were lost on heating to give single, broad melt endotherms due to coalescence of sample components. Furthermore, tannin stearate samples with high DS show relatively greater endothermic melting at higher temperature than those samples with lower DS. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Adenosyl Radical: Reagent and Catalyst in Enzyme Reactions

Adenosine is undoubtedly an ancient biological molecule that is a component of many enzyme cofactors: ATP, FADH, NAD(P)H, and coenzyme A, to name but a few, and, of course, of RNA. Here we present an overview of the role of adenosine in its most reactive form: as an organic radical formed either by homolytic cleavage of adenosylcobalamin (coenzyme B₁₂, AdoCbl) or by single‐electron reduction of S‐adenosylmethionine (AdoMet) complexed to an iron–sulfur cluster. Although many of the enzymes we discuss are newly discovered, adenosine's role as a radical cofactor most likely arose very early in evolution, before the advent of photosynthesis and the production of molecular oxygen, which rapidly inactivates many radical enzymes. AdoCbl‐dependent enzymes appear to be confined to a rather narrow repertoire of rearrangement reactions involving 1,2‐hydrogen atom migrations; nevertheless, mechanistic insights gained from studying these enzymes have proved extremely valuable in understanding how enzymes generate and control highly reactive free radical intermediates. In contrast, there has been a recent explosion in the number of radical‐AdoMet enzymes discovered that catalyze a remarkably wide range of chemically challenging reactions; here there is much still to learn about their mechanisms. Although all the radical‐AdoMet enzymes so far characterized come from anaerobically growing microbes and are very oxygen sensitive, there is tantalizing evidence that some of these enzymes might be active in aerobic organisms including humans.