Crystallization of barium diborate glass

The conditions for crystallization of a new modification of barium diborate in the glass of stoichiometric composition are investigated. This modification is characterized using X-ray diffraction analysis. In order for the -BaO 2B₂O₃ modification to crystallize, the glass should be purified from dissolved gases and have an undisturbed fire-polished surface. Otherwise, the modification crystallizes under the same conditions. The melting temperature of the -BaO 2B₂O₃ modification is determined to be T _melt = 805°C. Upon heating, the modification in the form of a powder transforms into the modification, whereas the modification in the form of a polycrystalline monolithic sample remains stable up to the melting temperature.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Polyakova, Pevzner.     

Synthesis and polymerization of 2-(β-N-3′-halogencarbazolylethyl)-2-oxazolines

Summary The synthesis of three novel oxazoline monomers,all of which contain 3-halogen substituted carbazolyl groups [i.e., 2-(-N-3 chlorocarbazolylethyl)-2-oxazoline, 2-(-N-3 bromocarbazolylethyl)-2-oxazoline and 2-(-N-3 iodocarbazolylethyl)-2-oxazoline]and their polymerization is described.     

X-ray absorption spectroscopy of Ti-containing molecular sieves ETS-10, aluminum-free Ti-β, and TS-1

We report here the first structural characterization by Ti K-edge EXAFS and XANES of ETS-10 and aluminum-free Ti- molecular sieves. A TS-1 sample was also studied for comparison. The near-edge spectrum of TS-1 revealed an intense pre-edge feature characteristic of Ti atoms in tetrahedral coordination. However, the pre-edge peak for ETS-10 was quite small and shifted in energy, which is consistent with the known octahedral structure surrounding Ti atoms in the material. Analysis of the EXAFS for ETS-10 revealed an average Ti-O interatomic distance of 2.00 +- 0.01 Å which is longer than the Ti-O distance (1.95Å) in anatase TiO₂. For Ti-, an intense pre-edge peak is present in the near-edge spectrum and the intensity, energy and width of this peak are the same as for TS-1. In addition, the average Ti-O interatomic distance in Ti- and TS-1 was 1.80 +- 0.01 Å, which is significantly shorter than the distance measured in ETS-10. The EXAFS and XANES results indicate that the Ti sites in aluminum-free Ti- are structurally identical to the tetrahedral sites in TS-1. This conclusion is supported by the similarity of the UV absorption thresholds for the two samples. X-ray absorption spectra were also recorded with methanol or 2-propanol adsorbed on the Ti- and TS-1 molecular sieves. Alcohol adsorption decreased the intensity and broadened the Ti pre-edge peak for both samples, demonstrating a local chemical interaction with the Ti sites. Methanol adsorption lengthened the average Ti-O bond to 1.83 ± 0.01 Å. The similarity of the X-ray absorption spectra for aluminum-free Ti- and TS-1 in the presence of alcohols suggests that the Ti sites in the two frameworks are chemically indistinguishable for vapor-phase adsorption of alcohols at low concentrations.     

Temperature programmed oxidation of Cu/ZnO catalysts with N2O: an attempt for characterization of copper catalysts

For characterization of the surface structure of metallic copper formed on the support, temperature programmed oxidation (TPO) with N₂O was carried out over various Cu/ZnO catalysts. Four peaks of the N₂ formation (, , and ) were observed at 223, 400, 545 and 600 K in the TPO runs. The average copper crystallite size estimated from the sum of the amount of - and -peaks agreed fairly with those determined by X-ray diffraction and transmission electron microscopy. It was concluded that - and -peaks resulted from the oxidation of metallic copper atoms on the steps, corners and/ or defect sites, and on the flat sites of the surface of copper crystallites, respectively, while - and -peaks resulted from the bulk oxidation of copper.     

Effect of heat treatment on corrosion and electrochemical behaviour of AZ91D magnesium alloy

An AZ91D ingot in the as-cast condition was homogenized by solution treatment and then aged for various periods of time. The microstructures produced were studied in detail and the phase volume fraction was measured quantitatively. The Corrosion resistance of all the different microstructures was studied in 3.5% NaCl solution through weight loss measurement in constant immersion conditions and potentiodynamic polarization experiments. The corroded surfaces were analysed using SEM and XRD. The volume fraction of the phase was found to have a significant influence on the corrosion behaviour. The T4 condition improved the corrosion resistance of AZ91D alloy compared to the T6 heat treatment. The results support the idea of microgalvanic coupling between cathodic phase and anodic matrix.     

Absorption of hydrogen in reduced nickel oxide

By repeated oxidation and reduction of nickel in alkaline solution an oxide film is formed on nickel which cannot be reduced further. In this film hydrogen is absorbed during cathodic polarization. The absorbed hydrogen is manifest in the voltammogram as an anodic peak before the Ni(OH)₂ peak. This was proved by H-diffusion experiments through nickel foils. From experiments with Ni electrodes covered with- or-Ni(OH)₂ films, it can be concluded that the reduced nickel oxide layer on nickel is most likely a-Ni(OH)₂ layer.     

X-ray diffraction study of anisotropy by formation and decomposition of nickel hydride Part I: Orientation dependence of the extent of phase transformation of nickel into nickel hydride

The effect of microstructure and crystal direction on the extent of phase transformation (EPT) of Ni into -NiH by cathodic charging with H has been investigated by X-ray diffraction. A measure for EPT in each crystal direction is the relevant volume fraction of -NiH. EPT is controlled by the crystal direction in the case of heat-treated specimens. In the case of electrodeposited specimens, the imperfections of which are commensurate with those of cold-worked metals, EPT is controlled by both the crystal direction and the dislocation-induced anisotropy at the same time. The study provides new information on the characteristics of the phase transformation of bulk nickel into -NiH.     

Additional male mediterranean fruitfly (Ceratitis capitata wied.) Attractants from Angelica seed oil (Angelica archangelica L.)

Two sesquiterpene hydrocarbons, -copaene and -ylangene, were isolated from bioactive fractions of angelica seed oil and were shown by field bioassays to be attractive to the male Mediterranean fruit fly. Their relative attractiveness, compared with the(+)-and (–)--copaene enantiomers, are: (+)--copaene>angelica -copaene>angelica -ylangene>(–)--copaene. The enantiomer ratios for the two compounds are: -copaene, 61.4% (+), 38.6% (–); -ylangene, 91.9% (+), 8.1% (–).trans--Bergamotene was also isolated from the same fractions, but in sufficient quantity for bioassay [enantiomer ratio: 95.7% (+), 4.3% (–)].     

Electroless nickel hydroxide: synthesis and characterization

An electroless method of nickel hydroxide synthesis through the complexation-precipitation route which yields a fine particle material having a specific surface area of 178 m² g^–1 has been described. The morphology of this material as revealed by electron microscopy is distinctly different from the turbostratic nature of electrosynthesized nickel hydroxide. While the long range structure as shown by the X-ray diffraction pattern is similar to that of -Ni(OH)₂, the short range structure as revealed by infrared spectroscopy incorporates characteristics similar to that of -Ni(OH)₂. Cyclic voltammetry studies show that the electroless nickel hydroxide has a higher coulombic efficiency (>90%), a more anodic reversible potential and a higher degree of reversibility compared to the electrosynthesized nickel hydroxide and conventionally prepared nickel hydroxide.     

X-ray diffraction study of anisotropy by the formation and decomposition of nickel hydride Part II: Decomposition kinetics

The role of the microstructure on the decomposition of -NiH formed as a result of the H cathodic charging of nickel was studied with the help of X-ray diffraction methods. This decomposition follows Kolmogorov-Avrami-Johnson-Mehl kinetics. The microstructural anisotropy induces anisotropy in the rate of phase transformation which is governed by the chemical reaction -NiHNi+H, i.e. it proceeds without diffusion limitations.     

Hydrogenation of C=C and C=O groups on ruthenium-tin catalysts

The effect of addition of tin on the catalytic activity of Ru/C catalysts has been investigated in the liquid phase hydrogenation of -methylstyrene and hydrocinnamaldehyde. On increasing the Sn content, the amount of CO chemisorbed decreases, indicating a decrease in the number of Ru surface atoms. In the hydrogenation of -methylstyrene the specific activity of Ru (calculated per Ru surface atom) remains constant regardless of the Sn/Ru ratio. An increase of specific activity is however observed in the hydrogenation of hydrocinnamaldehyde. It is suggested that tin, present mainly as Sn ions, enhances the reactivity of the C=O group.     

Immobilization of β-Glucosidase on carbon nanotubes

Carbon nanotubes are demonstrated as a good support for the immobilization of -Glucosidase. This is an enzyme with high molecular weight (ca. 135 kDa). A high enzyme loading of 630 mg per gram of support was achieved in 12 h. The link between the enzyme and the carbon nanotubes surface was by electrostatic interactions due to the different charges of the enzyme and the support at the pH of the immobilization. Immobilized -Glucosidase showed a catalytic activity above 400 U/g on the hydrolysis of 4-nitrophenyl--D-glucopyranoside (p-NPG).     

Effect of hydrogen on discharge behaviour of the nickel oxide electrode

The effect of hydrogen on the discharge behaviour of the nickel oxide electrode has been investigated in 30% KOH solution at 25°C. Open-circuit potentials of the nickel oxide electrodes, previously fully charged, decrease more rapidly in a hydrogen atmosphere than in an argon environment. Voltammograms of the nickel oxide electrode show that the amount of cathodic charge decreases considerably when the nickel oxide electrode is exposed to hydrogen rather than to argon. These results, along with X-ray diffraction data, indicate that hydrogen can increase the self-discharge rate of the nickel oxide electrode as a result of reduction of -NiOOH to -Ni(OH)₂ and the simultaneous oxidation of hydrogen. In addition, hydrogen can produce changes in the nickel oxide electrode during charge that persist to modify discharge behaviour and open-circuit potential.     

Response of the Seven-spot Ladybird to an Aphid Alarm Pheromone and an Alarm Pheromone Inhibitor is Mediated by Paired Olfactory Cells

Electrophysiological responses of adult seven-spot ladybirds, Coccinella septempunctata, to (E)--farnesene, an aphid alarm pheromone, and (–)--caryophyllene, a plant-derived alarm pheromone inhibitor, were investigated by recording from single olfactory cells (neurons) on the antenna. Cells having high specificity for each of the two compounds were identified. Furthermore, these two cell types were frequently found in close proximity, with a larger amplitude consistently recorded for the cell responding specifically to (E)--farnesene. Preliminary behavioral studies in a two-way olfactometer showed that walking adults were significantly attracted to (E)--farnesene; this activity was inhibited with increasing proportions of (–)--caryophyllene. The possible ecological significance of colocation or pairing of olfactory cells for semiochemicals with different behavioral roles is discussed.     

Growth behavior of Bacillus thuringiensis and production of poly(3-hydroxyalkanoates) on different organic substrates

Summary Bacillus thuringiensis is known as a bacterial species capable of the production of short side chain poly--hydroxyalkanoates (PHAs). In the present work it was shown that the organism is also capable of producing longer side chain PHAs under appropriate conditions. The microorganism was grown separately on glucose, nonanoic acid, and a mixture of glucose, peptone and casein in attempts to obtain poly--hydroxyalkanoates with varying lengths of the pendent alkyl group in the -position of the polymer repeat unit. The growth on glucose resulted in the formation of poly-3-hydroxybutyrate, (PHB), which is a very common bacterial storage polymer, while the utilization of nonanoic acid resulted in the formation of a copolymer consisting of 3-hydroxynonanoate and 3-hydroxyheptanoate units (PHN/PHH), which is the usual product of the microbial utilization of this particular carbon source by Pseudomonas oleovorans.     

Electrooxidation of β-D(+)glucose on bare and u.p.d. modified platinum particles dispersed in polyaniline

Platinum particles dispersed in a polyaniline film (PAni/Pt) provide a better catalyst than smooth Pt for the electrooxidation of -d(+)glucose in perchloric acid aqueous solutions. The Pt particles are less sensitive to poison formation than smooth platinum. Their catalytic activity is influenced by modification with underpotential deposition (u.p.d.) of thallium, lead or bismuth. Up to 0.4V vs RHE the Pt particles show a better activity than u.p.d.- modified platinum particles. However, above 0.4V the u.p.d.-modified particles are more active than bare Pt particles. Underpotential deposition of cadmium inhibits the electrooxidation of - d(+)glucose. The morphology and the nature of the metallic dispersion were examined by transmission electron microscopy.     

Sources of Variation in Concentration and Composition of Foliar Monoterpenes in Tamarack (Larix laricina) Seedlings: Roles of Nutrient Availability, Time of Season, and Plant Architecture

The effects of foliage class, time of season, and nutrient availability on monoterpene composition and concentration were evaluated. In the first experiment, we compared foliar monoterpenes of long shoots versus short shoots, which differ in age and origin, and differences due to nutrient availability and time of season. Both the concentrations and compositions of these monoterpenes were higher in the foliage of the long shoots. The only exceptions were the concentration of -3-carene and the composition of -pinene. Within a foliage class, the concentrations of seven monoterpenes and the percentages of five monoterpenes changed over the season. Of these, almost all declined, with the exceptions of -pinene and an unknown. Nutrient availability significantly affected the concentration or composition of some monoterpenes, but only to a slight extent. -Pinene and the unknown increased with nutrient availability, whereas -pinene and myrcene decreased. A more comprehensive analysis of four foliage classes on a separate cohort of trees showed that all monoterpenes, except sabinene and terpinolene, differed between foliage classes, but there were few general patterns. Overall, within-tree variation in tamarack monoterpenes related to foliage class and age appears more important than between-tree variation due to nutrient availability. These results suppport the view that products of mevalonic acid biosynthesis, such as terpenes, do not follow predictions of the carbon–nutrient balance and growth differentiation hypotheses. Our overall results show that individual hosts need to be considered as phytochemical mosaics when interpreting herbivore–plant interactions.     

Identification of host fruit volatiles from hawthorn (Crataegus spp.) attractive to hawthorn-origin Rhagoletis pomonella flies

Solid-phase microextraction (SPME) and gas chromatography coupled with electroantennographic detection (GC-EAD) were used to identify volatile compounds from hawthorn fruit (Crataegus spp.) acting as behavioral attractants for hawthorn-infesting Rhagoletis pomonella flies. Consistent EAD activity was obtained for six chemicals: ethyl acetate (94.3%), 3-methylbutan- 1-ol (4.0%), isoamyl acetate (1.5%), 4,8-dimethyl-1,3(E),7-nonatriene (0.07%), butyl hexanoate (0.01%), and dihydro--ionone (0.10%). In a flight-tunnel bioassay, there was a dose-related increase in the percentage of flies flying upwind to the six-component mixture. Hawthorn-origin flies also made equivalent levels of upwind flight with the synthetic blend and an adsorbent extract of volatiles collected from whole fruit, each containing the same amount of the 3-methylbutan-1-ol compound. Significantly lower levels of upwind flight occurred to a previously identified volatile blend of ester compounds that attracts R. pomonella flies infesting domestic apples, compared with the hawthorn volatile mix. Selected subtraction assays showed further that the four-component mixture of 3-methylbutan-1-ol, 4,8-dimethyl-1,3(E),7-nonatriene, butyl hexanoate, and dihydro--ionone also elicited levels of upwind flight equivalent to the six-component mix. Removal of 3-methylbutan-1-ol from the four-component blend resulted in complete loss of upwind flight behavior. Removal of dihydro- -ionone, 4,8-dimethyl-1,3(E),7-nonatriene, or butyl hexanoate from the four-component mixture resulted in significant decreases in the mean number of upwind flights compared to the four- or six-component mixtures.     

Factors governing the electrochemical synthesis of α-nickel (ii) hydroxide

The electrodeposition of -nickel hydroxide is promoted by the simultaneous chemical corrosion of the electrode by an acidic nitrate bath. Chemical corrosion results in the formation of a poorly ordered layered phase which is structurally similar to -nickel hydroxide and provides nucleation sites for the deposition of the latter. Therefore under conditions which enhance corrosion rates such as low current density (<1.3 mA cm–2), high temperature (60 C), high nickel nitrate concentration ( 1M) and the resultant low pH (1.7), -nickel hydroxide electrodeposition is observed, while -nickel hydroxide forms under other conditions. Further, -nickel hydroxide deposition is more facile on an iron electrode compared to nickel or platinum.     

Isolation and Structural Identification of a Germination Inhibitor in Fire-Recruiters from the California Chaparral

A role for inhibitors as regulators of seed dormancy in fire-dependent annuals and their nondormant (fire-independent) congeners was examined in the family Hydrophyllaceae. From seeds of the fire-dependent species, Emmenanthe penduliflora, Phacelia minor, P. brachyloba, and P. grandiflora, extracts were obtained that were found to be largely self-inhibitory and potent inhibitors of seed germination in nondormant congeners. Lower activity was detected in the fire-independent species, P. tanacetifolia and P. campanularia. The inhibitory activity was associated with the new sucrose ester, 6-O-linoleyl--D-glucopyranosyl--D-fructofuranoside.