The Influence of a Phase Transition in Poly(oxyethylene)/Poly(oxypropylene)/Poly(oxyethylene) Block Copolymer Surfactants on the Properties of Material Adsorbed from Dilute Aqueous Solution

In this study the adsorption of poloxamer block copolymer surfactants to polystyrene latex has been studied at a range of temperatures. It has been noted previously that the adsorption first falls, then rises and falls again as the temperature is increased, due to the existence of a phase transition in aqueous solutions of these surfactants at specific temperatures, which may be a critical micelle temperature. The present study shows that the hydrophobicity of the surface changes in a manner related to the amount of poloxamer adsorbed (i.e. is greatly influenced by the temperature of adsorption in relation to the transition temperature). The coating layer thickness, however, is essentially unchanged by the temperature of adsorption (i.e. not related to the amount adsorbed), but is influenced by the temperature at which the sizing was undertaken. This is due to dehydration of the poly (oxyethylene) with increasing temperature. The data presented here provide a possible explanation for the changes in biological distribution of poloxamer coated particles which occur when they are injected into animals.     

Arabidopsis ent-kaurene oxidase catalyzes three steps of gibberellin biosynthesis

The Arabidopsis GA3 cDNA was expressed in yeast (Saccharomyces cerevisiae) and the ability of the transformed yeast cells to metabolize ent-kaurene was tested. We show by full-scan gas chromatography-mass spectrometry that the transformed cells produce ent-kaurenoic acid, and demonstrate that the single enzyme GA3 (ent-kaurene oxidase) catalyzes the three steps of gibberellin biosynthesis from ent-kaurene to ent-kaurenoic acid.     

Prediction of the distribution of alkali and trace elements between the condensed and gaseous phases in a municipal solid waste incinerator

The FactSage thermodynamic calculation package and databases have been used to predict the equilibrium composition of the solid, liquid and gaseous products from municipal solid waste incineration. One series of calculations has considered the equilibrium for municipal waste combustion over a range of temperatures (850-1350 °C) that includes the typical combustion temperature of 950 °C and covers excursions to both lower and higher temperatures. A second set covers cooling of the combustion gas to 300 °C and the formation of condensates. However, it is recognised that the lower the temperature the greater the importance of kinetics and no attempt is made to deal with such topics as nucleation by pre-existing airborne particulates. Consideration is given to the effect of oxygen potential together with alkali, chlorine, and water content on the equilibrium products. Further calculations conceptualising “local equilibrium” around specific metal-containing items in the waste stream, for example a CRT tube, have illustrated how lack of global equilibrium, arising from non-uniformity in the burning bed could lead to atypical local metal distributions. Combined, these calculations provide a greater understanding of the behaviour of metals in municipal waste incineration than previous studies, accounting to some extent for the great variation in waste composition and local combustion conditions in a complex and variable industrial system.     

The flavohemoglobin of Escherichia coli confers resistance to a nitrosating agent, a "Nitric oxide Releaser," and paraquat and is essential for transcriptional responses to oxidative stress

Escherichia coli possesses a flavohemoglobin (Hmp), product of hmp, the first microbial globin gene to be sequenced and characterized at the molecular level. Although related proteins occur in numerous prokaryotes and eukaryotic microorganisms, the function(s) of these proteins have been elusive. Here we report construction of a defined hmp mutation and its use to probe Hmp function. As anticipated from up-regulation of hmp expression by nitric oxide (NO), S-nitrosoglutathione (GSNO) or sodium nitroprusside (SNP), the hmp mutant is hypersensitive to these agents. The hmp promoter is more sensitive to SNP and S-nitroso-N-penicillamine (SNAP) than is the soxS promoter, consistent with the role of Hmp in protection from reactive nitrogen species. Additional functions for Hmp are indicated by (a) parallel sensitivity of the hmp mutant to the redox-cycling agent, paraquat, (b) inability of the mutant to up-regulate fully the soxS and sodA promoters in response to oxidative stress caused by paraquat, GSNO and SNP, and (c) failure of the mutant to accumulate reduced paraquat radical after anoxic growth. We conclude that Hmp plays a role in protection from nitrosating agents and NO-related species and oxidative stress. This protective role probably involves direct detoxification of those species and sensing of NO-related and oxidative stress.     

Experimental analysis and modeling of buried waveguides fabricatedby quantum-well intermixing

The fabrication of buried waveguides in InP-based quantum-well (QW) material through the use of implantation. Enhanced QW band edge blue-shifting is reported. First, the lateral selectivity of implantation-induced QW intermixing is investigated using a specially designed implantation mask and photoluminescence. The refractive index change of the intermixed material is measured near the band edge. In combination, the lateral resolution and the index difference have allowed for the fabrication of narrow buried waveguides in an InP-based laser structure. Detailed modeling of the mode excitation and beam propagation of these devices is performed, and results are compared with experimental near-field profiles. We demonstrate that the waveguides are single-mode for both TE and TM polarizations at wavelengths near the band edge. The potential applications of this waveguide structure include post-growth fabrication of buried waveguide lasers and other integrated components     

Antecedents of flow in online shopping: a test of alternative models

Flow is an optimal state of experience that has been studied in various situations, including online environments. In such environments, it has been found to be positively related to exploratory behaviour, revisit and purchase intention, and positive attitude towards web sites. Based on flow theory, this study tests the complete structure of the flow model as it was originally formulated in an online shopping context. The role of the preconditions of flow is elaborated and the effect of web site complexity, an important interface design variable, on flow is examined. Results show that web site complexity affects flow through the mediating effects of the three preconditions of flow. Theoretical and practical implications of this finding are discussed.