Volatile Organic Compounds Emitted by Fungal Associates of Conifer Bark Beetles and their Potential in Bark Beetle Control

Conifer bark beetles attack and kill mature spruce and pine trees, especially during hot and dry conditions. These beetles are closely associated with ophiostomatoid fungi of the Ascomycetes, including the genera Ophiostoma, Grosmannia, and Endoconidiophora, which enhance beetle success by improving nutrition and modifying their substrate, but also have negative impacts on beetles by attracting predators and parasites. A survey of the literature and our own data revealed that ophiostomatoid fungi emit a variety of volatile organic compounds under laboratory conditions including fusel alcohols, terpenoids, aromatic compounds, and aliphatic alcohols. Many of these compounds already have been shown to elicit behavioral responses from bark beetles, functioning as attractants or repellents, often as synergists to compounds currently used in bark beetle control. Thus, these compounds could serve as valuable new agents for bark beetle management. However, bark beetle associations with fungi are very complex. Beetle behavior varies with the species of fungus, the stage of the beetle life cycle, the host tree quality, and probably with changes in the emission rate of fungal volatiles. Additional research on bark beetles and their symbiotic associates is necessary before the basic significance of ophiostomatoid fungal volatiles can be understood and their applied potential realized.     

Crystal structure of the bacterial ribosomal decoding site complexed with a synthetic doubly functionalized paromomycin derivative: a new specific binding mode to an a-minor motif enhances in vitro antibacterial activity

The crystal structure of the complex between oligonucleotide containing the bacterial ribosomal decoding site (A site) and the synthetic paromomycin analogue 1, which contains the gamma-amino-alpha-hydroxybutyryl (L-haba) group at position N1 of ring II (2-DOS ring), and an ether chain with an O-phenethylaminoethyl group at position C2' of ring III, is reported. Interestingly, next to the paromomycin analogue 1 specifically bound to the A site, a second molecule of 1 with a different conformation is observed at the crystal packing interface which mimics the A-minor interaction between two bulged-out adenines from the A site and the codon-anticodon stem of the mRNA-tRNA complex. Improved antibacterial activity supports the conclusion that analogue 1 might affect protein synthesis on the ribosome in two different ways: 1) specific binding to the A site forces maintenance of the "on" state with two bulged out adenines, and 2) a new binding mode of 1 to an A-minor motif which stabilizes complex formation between the ribosome and the mRNA-tRNA complex regardless of whether the codon-anticodon stem is of the cognate or near-cognate type.     

Melt rheology and morphology of physically compatibilized natural rubber–polystyrene blends by the addition of natural rubber-g-polystyrene

Blends of natural rubber (NR) and polystyrene (PS) were prepared by melt mixing in a Brabender plasticorder and by solution casting using chloroform as the casting solvent. Earlier studies have indicated that these blends are incompatible and immiscible, and their compatibility can be improved by the addition of a graft copolymer of NR and PS (NR-g-PS). The rheological behavior of these blends has been carried out in the presence and absence of the compatibilizer using a capillary rheometer and a melt flow indexer. The effects of blend ratio, processing techniques (melt mixing versus solution casting), shear stress, and temperature on the rheological behavior have been studied in detail. Both in the presence and absence of the copolymer, the blends showed a decrease in viscosity with an increase of shear stress, indicating pseudoplastic nature. Solution-cast blends showed a higher viscosity as compared to melt-mixed blends. The viscosity versus composition curve of both melt-mixed and solution-cast blends showed negative deviation from the additivity at a higher shear rate region. This is associated with the interlayer slip between the highly incompatible NR and PS phases. The effects of graft copolymer loading and temperature on solution-cast blends were studied, and it was found that as the copolymer loading increases, the shear viscosity increases. This is due to the high interfacial interaction between the two components in the presence of the copolymer. The copolymer, in fact, locates at the interface and makes the interface more broad. However, at higher loading of the copolymer, the viscosity of the blends decreases. This may be associated with the formation of micelles, which have a plasticizing action on the viscosity of the blends. Melt elasticity parameters like principal normal stress difference, recoverable elastic shear strain, and die swell were evaluated. Master curves have been generated using modified viscosity and shear rate functions that contain the melt flow index as a parameter. The extrudate morphology of the blends was studied using a scanning electron microscope. Addition of the copolymer reduces the domain size of the dispersed phase, followed by a leveling off at a higher concentration. The leveling off is an indication of interfacial saturation. The interparticle distance also decreased followed by a leveling off at a higher loading of the copolymer. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2673–2690, 1998     

Dielectric spectroscopic studies on polypyrrole glucose oxidase films

An investigation was made into the dielectric spectroscopic characteristics of p-toluene sulfonate (PTS) doped polypyrrole (PPY) films in the presence and absence of immobilized glucose oxidase (GOX) in three different configurations: Al-PTS-PPY-Al-PTS-PPY/GOX-Al, and Al-PTS-PPY/GOX/β-D -glucose-Al, respectively. Measurement of dielectric loss and capacitance yielded valuable information about the dielectric properties of GOX immobilized in PTS doped PPY films. The effect of both the temperature and varying βD -glucose concentrations on the mobility of the charge carriers in these films was also systematically studied. © 1996 John Wiley & Sons, Inc.     

Pervaporation of chlorinated hydrocarbon-acetone mixtures through poly(ethylene-co-vinyl acetate) membranes

Crosslinked and uncrosslinked ethylene-vinyl acetate copolymer membranes were prepared. The permeation characteristics in the pervaporation process were examined using carbon tetrachloride-acetone mixtures. Modified membranes exhibit carbon tetrachloride permselectivity, but unmodified membranes did not display the permselectivity of crosslinked polymer. Furthermore, membranes modified with dicumyl peroxide (DCP) showed a higher flux and selectivity than those of benzoyl peroxide (BP) modified ones. The effects of feed concentration, molecular size, and polarity of the permeating species on pervaporation were analyzed. The influence of crosslinking density of the membranes on pervaporation was also analyzed. The maximum separation and flux were found to be associated with an optimum amount of crosslinking agent in the membrane. A mixture of chloroform and acetone having a composition near the azeotropic region was also separated by the pervaporation technique. © 1996 John Wiley & Sons, Inc.     

Investigation on Phase Change Behavior of Paraffin Phase Change Material in a Spherical Capsule for Solar Thermal Storage Units

In this work, the melting and solidification behaviour of paraffin phase change material encapsulated in a stainless steel spherical container has been studied experimentally. A computational fluid dynamics analysis has also been performed for the encapsulated phase change material (PCM) during phase change process. In the melting process, the hot air, used as the heat transfer fluid enters the test section and flows over the spherical capsule resulting in the melting of phase change material. In the solidification process, the ambient air flows over the capsule and received heat from phase change material resulting in the solidification of phase change material. In the computational fluid dynamics, the constant wall boundary condition is employed for both melting (75°C) and solidification (36°C) processes since the internal conductive resistance offered by the PCM is much higher compared to the outer surface convective resistance. The time required for complete solidification and melting of the phase change material obtained from the computational fluid dynamics analysis are validated with the experimental results and a reasonable agreement is achieved. The reason for the deviation between the results are analyzed and reported.     

Can the degree of crystallinity of ball-milled Mg2Ni intermetallic compound decide its electrochemical characteristics?

ABSTRACT

Nanostructured Mg₂Ni intermetallic compounds were synthesized by high-energy ball milling. Effect of milling time on structure and surface morphology of milled powders were studied using x-ray diffraction and scanning electron microscopy. Crystallite size and degree of crystallinity were confirmed by using transmission electron microscopy and selected area electron diffraction analysis. The particle size of 20 h milled electrode material is 230 nm and it reduced to 40 nm when the milling time is increased to 30 h. Further increase in the milling time reduces the particles size drastically and starts agglomerating. In order to understand the effect of milling time on reaction rates, differential thermal analysis was performed. Activation energy of the milled powders was calculated using Kissinger analysis. 30 h milled powder exhibits lower activation energy than others. Cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge studies were done on the prepared electrode materials. 30 h milled electrode material delivers maximum discharge capacity with a superior capacity retention after 20 cycles at 20 mAg^?1.