Managing Nitrate Problems for Domestic Wells in Irrigated Alluvial Aquifers

Many irrigated areas in the United States and abroad overlie unconfined aquifers. The soils are coarse textured with low water-holding capacity, and irrigation water is frequently necessary for crop growth. Many of these areas experience elevated nitrate levels in water from shallow domestic wells. It is often observed that the nitrate plumes are stratified with depth with the highest concentration just near the surface. The irrigation wells are generally screened toward the bottom part of the aquifer where the material is coarse and the available drawdown is greater. Pumpage is typically cyclic but can be somewhat continuous during drought conditions. It is often believed that the floating nitrate plume is recycled by the irrigation wells. Simulations were carried out to show that slight deepening of domestic wells in both stratified and more homogeneous aquifers could eliminate nitrate problems for many domestic wells even in close proximity of irrigation wells.     

Kinetic study of olefin polymerization with a supported metallocene catalyst. III. Ethylene homopolymerization in slurry

A kinetic study of ethylene homopolymerization is conducted with a supported unbridged metallocene catalyst in a slurry reactor. The effects of operational parameters such as the reaction temperature and pressure on kinetics are investigated. The kinetic parameters which have been determined for this particular catalyst from previous gas phase studies are used in a slurry reactor model to predict the polymerization behavior under various reaction conditions. The experimental data compare favorably with the predictions from this model. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2901–2917, 2001     

Acoustic emission during monotonic and cyclic fracture toughness tests of 304LN weldments

Determination of initiation fracture toughness of ductile materials is a challenging task due to the ambiguity associated with the identification of the point of departure of the initial linear region of the fracture resistance curve. Acoustic emission (AE) is a technique that is capable of directly indicating the crack initiation point during fracture toughness tests using a single specimen. The objective of this investigation is to illustrate some results related to monotonic and cyclic fracture behaviour of AISI 304LN weldments estimated by this ‘combined type’ experiment. The use of cyclic J-integral tests has been proposed to simulate the deleterious effect of periodic load reversals during monotonic loading. A comparative analysis of all these data leads to the conclusion that the fracture toughness of a material determined from AE parameters is generally conservative compared to that obtained by conventional techniques.     

2,3-Hexanediols as Sex Attractants and a Female-produced Sex Pheromone for Cerambycid Beetles in the Prionine Genus Tragosoma

Recent work suggests that closely related cerambycid species often share pheromone components, or even produce pheromone blends of identical composition. However, little is known of the pheromones of species in the subfamily Prioninae. During field bioassays in California, males of three species in the prionine genus Tragosoma were attracted to 2,3-hexanediols, common components of male-produced aggregation pheromones of beetles in the subfamily Cerambycinae. We report here that the female-produced sex pheromone of Tragosoma depsarium “sp. nov. Laplante” is (2R,3R)-2,3-hexanediol, and provide evidence from field bioassays and electroantennography that the female-produced pheromone of both Tragosoma pilosicorne Casey and T. depsarium “harrisi” LeConte may be (2S,3R)-2,3-hexanediol. Sexual dimorphism in the sculpting of the prothorax suggests that the pheromone glands are located in the prothorax of females. This is the second sex attractant pheromone structure identified from the subfamily Prioninae, and our results provide further evidence of pheromonal parsimony within the Cerambycidae, in this case extending across both subfamily and gender lines.     

The impact of nanoclay on the crystal growth kinetics and morphology of biodegradable poly(ethylene succinate) composite

The impact of nanoclay on the isothermal crystal growth kinetics and morphology of biodegradable poly(ethylene succinate) (PES) is reported. A PES composite (PESNC) containing 5 wt% organically modified montmorillonite, was prepared via solvent casting method. The structural study of PESNC, using X-ray diffraction and optical microscope, showed the formation of micro-intercalated composite. The isothermal crystallization behavior of neat PES and PESNC was studied by differential scanning calorimetry, polarized optical and atomic force microscopes. Results show that the supercooling effect of neat PES reduces after composite formation. The Lauritzen–Hoffman secondary nucleation theory (the LH-model) was employed to understand the crystal growth mechanism of these systems. According to the LH-model, only one transition between regime II and regime III was found, but no transition from regime I to II was detected.     

Non-destructive ultrasonic evaluation of CFRP–concrete specimens subjected to accelerated aging conditions

The objective of this work is to utilize surface acoustic waves (SAWs) for non-destructive structural health monitoring of concrete specimens externally bonded with carbon fiber-reinforced polymer (CFRP) composites and subjected to accelerated aging conditions. Both experimental testing and signal processing schemes of ultrasonic wave propagation through the CFRP substrate are described. The surface waves are generated and received at the external face of the CFRP using narrow-band transducers with a 110-kHz center frequency. The received signals are filtered and amplified then digitized and processed to extract various parameters in both time and frequency domains including average power (P_Avg), maximum amplitude (V_max), and maximum power–frequency ratio ((P/F)_max). Changes in these parameters due to water-immersion aging at different temperatures were monitored over 12 weeks. Results indicated a marked decrease in measured ultrasonic parameters over time, particularly after the first 2 weeks, indicating a possible debonding or deterioration in the samples. Ultrasonic results showed good agreement with the findings of a parallel destructive study on mode-II fracture loading of CFRP–concrete samples, tested to obtain fracture energy (G_f) and define traction–separation response under temperature and water-immersion aging effects. It was observed that all ultrasonic parameters exhibit good correlations (|r|>0.5, P<0.05) with the fracture energy at all temperatures. Moreover, when the measurements at all temperatures were incorporated and linear relationships between destructive and non-destructive parameters were assumed, correlations of r=0.84, 0.80, and 0.80 were found between G_f and P_Avg, V_max, and (P/F)_max, respectively. This study paves the way for developing a non-destructive testing protocol for structural health monitoring of bridges and concrete structures undergoing repair and rehabilitation with CFRP composites.     

A novel rock-like nanoarchitecture of YVO4:Eu3+ phosphor: selective synthesis, characterization, and luminescence behavior

A facile, surfactant-mediated strategy involving ‘oriented attachment’ assisted self-assembly of rice-like and grape-like nanostructures resulted into a novel encapsulated rock-like luminescent YVO₄:Eu³⁺ nanoarchitecture in aqueous medium. It is shown that a characteristic crystallization behavior of YVO₄:Eu³⁺ leads to the growth of a rice-like shape in a template-free reaction system. In presence of a surfactant, these rice-like structures in the vicinity of the micellar head groups self-assemble to form nanograpes and ultimately produce rock-like nanostructures upon prolonged autoclaving. The rock-like nanocrystalline phosphors, having an average area of 2798 nm², are composed of an inner nucleus and a surrounding shell-like cover, as evidenced from the transmission electron microscopy images. Finally, the room temperature photoluminescence spectra demonstrate that the morphology of the nanophosphors has immense influence on their chromaticity.     

A miniature microbial fuel cell operating with an aerobic anode chamber

A miniature microbial fuel cell (mini-MFC) is described that utilizes an aerobic culture of Shewanella oneidensis DSP10 as the active electrochemical species in the anode chamber. We find that the maximum aerobic mini-MFC power without the addition of exogenous mediators was 0.40 mW, a 33% decrease when compared with an anaerobic DSP10 culture (0.6 mW) operating in the mini-MFC. This decrease is most likely due to the presence of dissolved oxygen in the anode chamber that scavenges electrons to form water, thereby reducing the number of electrons donated to the anode. Aerobic power and current density at maximum power using the true surface area of the anode (611 cm²) were calculated to be 6.5 mW m⁻² and 13 mA m⁻². The power density rises to 2.0 W m⁻² and 330 W m⁻³ when calculated using the cross-sectional area and volume of the device (2 cm², 1.2 cm³). The Coulombic efficiency was also reduced from 11 to 5% when using the aerobic versus anaerobic culture. Similar results were found when the external mediator anthraquinone-2,6-disulfonate (AQDS) was added to the aerobic culture, resulting in a maximum power of 0.54 mW, a 37% drop in power when compared to the anaerobic mediated system.