Pheromone biosynthesis in lepidoptera

Pheromone components for many lepidopteran species are produced by the use of unique chain-shortening and 9, 10, and 11 desaturase systems. Correlations in the Tortricidae indicate that the pheromone components derived from 9 and 01 desaturases are found in the more primitive species (those possessing morphological plesiomorphies). The precise blend ofZ andE acetates in a number of species is regulated in the final reduction sequence from acyl intermediates. Preliminary research has been conducted on the characterization of the various desaturase enzymes used and on the important blend regulating sequence. Initial purification work on the 11 desaturase enzyme found in the cabbage looper moth is reported.     

The solubility of CO2 in triethylene glycol monomethyl ether

The solubility of CO₂ in triethylene glycol monomethyl ether (TEGMME) has been measured at 40, 70 and 100°C at pressures up to 8.8 MPa. The results were correlated with the Peng-Robinson (1976) equation of state. The interaction parameters and Henry's constants were derived.     

Off-line optimization and control for real time integration of a three-phase hydrogenation catalytic reactor

In order to develop and test the integration procedure, in this paper a real time process integration involving the optimization and control of the process is presented, in this case, with the two-layer approach. The used optimization algorithms were Levenberg–Marquardt and SQP that solve a non-linear least square problem subject to bounds on the variables. The two-layer approach is a hierarchical control structure where an optimization layer calculates the set points and manipulated variables to the advanced controller, which is based on the dynamic matrix control with constraints (QDMC). The non-isothermal dynamic model of the three-phase slurry catalytic reactor with appropriate solution procedure was utilized in this work (Vasco de Toledo, E. C., Santana, P. L., Maciel, M. R. W., & Maciel Filho, R. (2001). Dynamic modeling of a three-phase catalytic slurry reactor. Chemical Engineering Science, 56, 6055–6061). The model consists on mass and heat balance equations for the catalyst particles as well as for the bulk phases of gas and liquid. The model was used to describe the dynamic behavior of hydrogenation reaction of o-cresol to obtain 2-methil-cyclohexanol, in the presence of a catalyst Ni/SiO₂.     

Surface Modification of Titania Nanoparticles Using Ultrathin Ceramic Films

Surface modification of titania nanoparticles was achieved by coating them with ultrathin alumina films using atomic layer deposition. The coating process was performed in a fluidized bed reactor at low pressure and under mechanical vibration. Films were deposited using self-limiting, sequential surface reactions of trimethylaluminum and water. The composition of alumina-coated particles was verified using infrared spectroscopy. The deposited films had an average growth rate of 0.2 nm/coating cycle and were highly uniform and conformal as demonstrated by transmission electron microscopy and X-ray spectroscopy. Deposited alumina films were amorphous as verified through X-ray diffraction and high-resolution electron microscopy. The coating process did not promote particle sintering as validated via particle size and surface area analysis.     

Transient and isotopic studies of the oxygen transport and exchange during oxidative coupling of methane on Sr promoted La2O3

Isotopic transient techniques were applied to study oxidative coupling of methane over lanthanum oxide and strontium promoted La₂O₃ catalysts. Results of the¹⁸O₂/¹⁶O₂ isotopic exchange experiments indicate that Sr promotion increases oxygen uptake from the lattice of the catalyst. Oxygen self diffusion coefficients, which were determined for the series of lanthana catalysts, reach a maximum for the 1% Sr/La₂O₃. Steps of¹⁸O₂ in the presence of a steady flow of methane over Sr/La₂O₃ catalysts, indicate that surface and bulk oxygen appear in the reaction products before gas-phase¹⁸O². Steps of CO₂ over catalysts in which lattice oxygen has been exchanged with¹⁸O₂, show that gas/solid exchange involves over 50% of the lattice oxygen. Under reaction conditions, methane pulses with no gas-phase oxygen yield negligible amounts of products which indicates that methane interacts with lattice oxygen only in the presence of the gas-phase oxygen.     

Electrically conductive adhesives: Effect of particle composition and size distribution

The effects of particle composition and size distribution on the electrical properties of conductive adhesives were studied. Silver-plated glass and silver-plated nickel particles with both narrow (37-44 μm) and broad (< 44 μm) size distributions were dispersed in an epoxy matrix. In all cases, formulations incorporating narrow particle size distributions required greater concentrations of particles to exceed the percolation threshold for electrical conduction than when broad particle distributions were used. Differences between glass and nickel particles were observed and attributed to the higher density of nickel particles, as well as subtle variations in particle size distributions.     

A predicted three-dimensional structure of human cytochrome P450: implications for substrate specificity

A three-dimensional structure for human cytochrome P450IA1 waspredicted based on the crystal coordinates of cytochrome P450camfrom Pseudomonas putida. As there was only 15% residue identitybetween the two enzymes, additional information was used toestablish an accurate sequence alignment that is a prerequisitefor model building. Twelve representative eukaryotic sequenceswere aligned and a net prediction of secondary structure wasmatched against the known -helices and ß-sheets ofP450cam. The cam secondary structure provided a fixed main-chainframework onto which loops of appropriate length from the humanP450IA1 structure were added. The model-built structure of thehuman cytochrome conformed to the requirements for the segregationof polar and nonpolar residues between the core and the surface.The first 44 residues of human cytochrome P450 could not bebuilt into the model and sequence analysis suggested that residues1–26 formed a single membrane-spanning segment. Examinationof the sequences of cytochrome P450s from distinct gene familiessuggested specific residues that could account for the differencesin substrate specificity. A major substrate for P450IA1, 3-methyl-cholanthrene,was fitted into the proposed active site and this planar aromaticmolecule could be accommodated into the available cavity. Residuesthat are likely to interact with the haem were identified. Thesequence similarity between 59 eukaryotic enzymes was representedas a dendrogram that in general clustered according to genefamily. Until a crystallographic structure is available, thismodel-building study identifies potential residues in cytochromeP450s important in the function of these enzymes and these residuesare candidates for site-directed mutagenesis.     

CO2‐assisted polymer processing: A new alternative for intractable polymers

CO₂‐assisted polymer processing is proposed as an alternative route for intractable and high molecular weight polymers based on the plasticization effects of CO₂ and its direct effect on the melting behavior of semicrystalline polymers. A modified processing system was used to process a variety of polymers in the presence of high‐pressure CO₂. The system includes an extruder that was modified to allow for high pressures created by the injection of CO₂. The new design includes a modified feed section that allows a given mass of polymer to interact with CO₂ before and during the extrusion process. The inherent shear mixing and the presence of CO₂ allow for a specific control over the extrudate morphology. Results suggest that this alternative design provides a new and easy route to melt process high melt viscosity polymers of commercial importance, such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer (FEP), and syndiotactic polystyrene (s‐PS). The increased processability of these systems in CO₂ is related to the plasticization effect of CO₂ that was quantified through a depression in the glass‐transition temperature according to the Chow model. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1501–1511, 2004     

Carbonization and liquid crystal (mesophase) development. 14. Co-carbonization of coals with A240 Ashland petroleum pitch: effects of conditions of carbonization upon optical textures of resultant cokes

This study examines the effect of pitch concentration, rate of heating, soak temperature and time of soak upon the optical texture of cokes prepared from the co-carbonizations of a coal (Oxcroft-Clowne, NCB Rank 802) and three vitrains of NCB Rank 204, 801, 902 with Ashland A240 petroleum pitch. Using the coal (Rank 802) with 10 wt % and 25 wt % additions of pitch caused progressive penetration of the pitch into the coal with a resultant development of a mozaic anisotropy in the coke to replace partially the original coke isotropy. With 50 wt % addition of pitch almost all of the coal particles, 600 to 1100 μm in size, were modified during carbonization. Some pitch coke was formed. For the coal and three vitrains with increasing rates of co-carbonization from 0.5–10 K min^?1 to 1200 K, using 25 wt % of A240 pitch, resultant cokes showed progressively increased extents of modification. For the two vitrains (Rank 801, 902) soaking at temperatures of 650–690 K caused a decrease in the extent of modification of isotropic coke when compared with the coke of HTT 1200 K. Evidently fast heating rates create the conditions of fluidity necessary for the pitch to modify the coal leading to growth of mesophase and anisotropic coke.     

Quantitation of the human basal ganglia with positron emission tomography: a phantom study of the effect of contrast and axial positioning

The accurate measurement of the concentration of a radioisotope in small structures with positron emission tomography (PET) requires a correction for quantitation loss due to the partial volume effect and the effect of scattered radiation. To evaluate errors associated with measures in the human basal ganglia (BG), a unilateral model of the BG has been inserted in a 20-cm cylinder. The recovery coefficient (RC=measured activity/true activity) for the BG phantom has been measured on a CTI tomograph with different background concentrations (contrast) and at different axial locations in the gantry. The BG was visualized on four or five slices, depending on its position in the gantry and on the contrast used. The RC was 0.75 with no background (contrast equal to 1.0). Increasing the relative radioactivity concentration in the background increased the RC from 0.75 to 2.00 when the contrast was -0.7 (BG相似文献