Rheology of whey protein isolate-xanthan mixed solutions and gels. Effect of pH and xanthan concentration

Flow properties at pH 5.5-7.5 of whey protein isolate (WPI)-xanthan solutions containing 0-0.5 w/w% xanthan were studied by viscosimetry, although rigidity and fracture properties of the corresponding heat-set gels (90°C, 30 min) were determined by uniaxial compression. All the studied solutions displayed generalized shearthinning flow behaviour. Synergistic WPI-xanthan interactions has been revealed by observing that rheological parameters [σ_msf, K, n, η (γ)] characterizing blends were larger than those calculated from the two separated solutions. Such a behaviour was attributed to segregative phase separation of whey proteins and xanthan. Effects of xanthan on WPI-xanthan gel properties both depended on pH and xanthan concentration. Simultaneous increased xanthan concentration and decreased pH inhibited gelation of WPI-xanthan blends. Regarding gel strength, synergistic WPI-xanthan interactions were observed at pH >7.0 and low xanthan concentration (0.05 or 0.1 w/w%). Antagonism between the two macromolecules occurred at low xanthan concentration and pH ≤6.5, and high xanthan concentration (0.2 or 0.5 w/w%) at all pH tested. Low xanthan concentration rendered mixed gels more brittle than protein gels, and high xanthan concentration decreased pH effects on gel stress-strain relationships. The balance between strong thermal aggregation of concentrated whey proteins - in presence of incompatible xanthan -, high viscosity of blends and repulsive surface forces of protein molecules was thought to be at the origin of WPI-xanthan gel mechanical properties.     

2-D mode tapering via tapered channel waveguide segmentation

A simple and versatile 2-D mode-tapering method for a channel waveguide, which is based on tapered waveguide segmentation, is proposed. The taper can be incorporated into the waveguide at the stage of lateral channel definition. The method is compatible with both mask photolithoography and direct writing techniques, and no modification of the transverse index profile is required.<>     

Amplified spontaneous emission and Rayleigh backscattering instrongly pumped fiber amplifiers

Amplified spontaneous emission (ASE) and Rayleigh backscattering (RBS) in strongly pumped fiber amplifiers are studied, employing a rate equation model. Approximate expressions for the ASE and RES, as well as for the amplifier noise figure are derived, based on approximate analytical expressions for the amplified signal, which are valid for both three-level and four-level systems. Numerical examples for rare-earth-doped fibers, show good agreement between these approximate expressions and the exact numerical solutions for strong pumping and for injected signals which are not too weak     

Strongly pumped fiber lasers

Strongly pumped fiber lasers are analyzed, based on a rate equation model. Examples include Nd³⁺-doped and Yb³⁺ -doped fiber lasers, with distributed Bragg reflector mirrors at either end. Approximate analytical and quasi-analytical expressions are shown to be in excellent agreement with the exact numerical solution of the rate equations, and both agree well with recently published experimental data     

CHEMICAL BASIS OF MIDDLE DISTILLATE FUEL INSTABILITY: Interactive Effects of Selected Nitrogen Heterocycles with Organic Bases in a Shale-Derived Diesel Fuel.

Fuel instability reactions are defined in terms of the formation of deleterious products such as filterable sediments and peroxides. Gravimetric stability tests have been carried out at 80^°C using two model nitrogen heterocycles: 2,5-dimethy1pyrrole, DMP, and 3-methylindole, 3-MI, in an otherwise stable shale derived middle distillate fuel. Potential interactive effects for these model nitrogen heterocycles have been described by the presence of organic base co-dopants. Organic bases employed included: tri-n-butylamine, N, N-dimethyl-aniline, and 4-dimethylaminopyridine. Simple organic amines exerted only minor interactive effects, usually an increase in filterable sediment in the range of 5-15%. However, the diamine species, 4-dimethylaminopyridine, interacted in a strong positive fashion to generate increased amounts, 22-44%, of sediment.     

Developmental changes in glucocorticoid receptor and 11beta-hydroxysteroid dehydrogenase oxidative and reductive activities in rat Leydig cells

Glucocorticoids directly regulate testosterone production in Leydig cells through a glucocorticoid receptor (GR)-mediated repression of the genes that encode testosterone biosynthetic enzymes. The extent of this action is determined by the numbers of GR within the Leydig cell, the intracellular concentration of glucocorticoid, and 11beta-hydroxysteroid dehydrogenase (11betaHSD) activities that interconvert corticosterone (in the rat) and its biologically inert derivative, 11-dehydrocorticosterone. As glucocorticoid levels remain stable during pubertal development, GR numbers and 11betaHSD activities are the primary determinants of glucocorticoid action. Therefore, in the present study, levels of GR and 11betaHSD messenger RNA (mRNA) and protein were measured in rat Leydig cells at three stages of pubertal differentiation: mesenchymal-like progenitors (PLC) on day 21, immature Leydig cells (ILC) that secrete 5alpha-reduced androgens on day 35, and adult Leydig cells (ALC) that are fully capable of testosterone biosynthesis on day 90. Numbers of GR, measured by [3H]dexamethasone binding, in purified cells were 6.34 +/- 0.27 (x 10(3) sites/cell; mean +/- SE) for PLC, 30.45 +/- 0.74 for ILC, and 32.54 +/- 0.84 for ALC. Although GR binding was lower in PLC, steady state levels for GR mRNA were equivalent at all three stages (P > 0.05). Oxidative and reductive activities of 11betaHSD were measured by assaying the conversion of radiolabeled substrates in incubations of intact Leydig cells. Both oxidative and reductive activities were barely detectable in PLC, intermediate in ILC, and highest in ALC. The ratio of the two activities favored reduction in PLC and ILC and oxidation in ALC (oxidation/reduction, 0.33 +/- 0.33 for PLC, 0.43 +/- 0.05 for ILC, and 2.12 +/- 0.9 for ALC, with a ratio of 1 indicating equivalent rates for both activities). The mRNA and protein levels of type I 11betaHSD in Leydig cells changed in parallel with 11betaHSD reductive activity, which increased gradually during the transition from PLC to ALC, compared with the sharp rise that was seen in oxidative activity. We conclude that Leydig cells at all developmental stages have GR and that their ability to respond to glucocorticoid diminishes as net 11betaHSD activity switches from reduction to oxidation. This provides a mechanism for the Leydig cell to regulate its intracellular concentration of corticosterone, thereby varying its response to this steroid during pubertal development.     

Geotechnical field applications of AE/MS techniques at the Pennsylvania State University: a historical review

Since the early 1970s there has been an accelerating interest in the use of acoustic emission/microseismic (AE/MS) techniques for the laboratory and field investigation of geological materials and structures. Basic AE/MS research and the application of AE/MS techniques to a variety of geotechnical problems has been under way in the Penn State Rock Mechanics Laboratory since 1965. To date, studies have involved a wide variety of field topics, including: cavern stability, stability of natural gas storage reservoirs, strata control in longwall coal mines, rock bolt stability monitoring, effects of blasting, mine and tunnel roof stability, subsidence monitoring and rock slope stability evaluation. This paper reviews the development of AE/MS research at Penn State, describes briefly a number of the major field studies undertaken, and discusses on-going and future research programmes.     

Personal communications services

The history of the US Federal Communications Commission (FCC) examination of proposals to allocate radio frequency spectrum to a new and innovative range of services it calls personal communications services (PCS) is outlined. Personal communication networks (PCN), which will supply mobile two-way, mass-market communications services, the most advanced offering of the PCS area, and spectrum allocation for PCS are discussed. The results of a consumer market study of the potential for PCN services are also discussed