Pricing Differentiated Services in the GPRS Environment

The General Packet Radio Service extends the existing GSM mobile communications technology by providing packet switching and higher data rates in order to efficiently access IP-based services in the Internet. We adapt the Differentiated Services Quality-of-Service support framework and apply it over the GPRS air interface in order to provide various levels of service differentiation. We also focus on applying a charging technique so as to publish a unit price for each service class. These prices are designed to lead to the maximization of social welfare and the users' net benefit.     

Dielectric and morphological investigations of phase separation and cure in rubber-modified epoxy resins: Comparison between teta- and DDM-based systems

Real-time and equilibrium dielectric measurements, covering the frequency range 10^?1–10⁵ Hz, are reported on a series of rubber-modified epoxy resins, based on reaction of the diglycidyl ether of bisphenol A (DGEBA) with either triethylenetetramine (TETA) or diaminodiphenylmethylene (DDM). The rubber modifier used was a carboxyl-terminated butadiene acrylonitrile (CTBN) reactive oligomer and the phase-separated structure, the results of which was examined using both dielectric and electron microscopic techniques. The mixture was initially homogeneous, but after a short period of time, it underwent phase separation and this process was marked by the appearance of a dielectric peak associated with ion-charge migration within the occluded rubbery phase. Analysis of the peak provided information on the morphology of the system and these data were compared with information obtained from scanning electron microscopy. A phase-separated morphology was observed consisting of spherical rubber particles dispersed in an epoxy matrix. For high concentrations of rubber ≥ 10 wt %, precipitation of epoxy domains within the rubbery phase was observed. Detailed dielectric studies of the peak associated with phase separation revealed that in the case of the TETA system the peak continued to shift after vitrification, whereas in the case of DDM, it was invariant with time. The point at which the peak appears was used to determine the time at which phase separation occurred. Differences observed in the lower temperature dielectric spectra were associated with variations in the form of the phase structure and possibly reflect different degrees of densification of the matrix. Good agreement was observed between the predictions of the Maxwell—Wagner—Sillers (MWS) theory and experimental observation for these systems. © 1993 John Wiley & Sons, Inc.     

Effects of the excluded volume interactions on the conformational properties of star polymers

The effects of the excluded volume interactions on the conformational properties of star polymers have been studied. First order calculations at the critical dimensionality d = 4 yield the critical exponents of the average quantities up to first order in ε = 4-d. We thus find the partition function, the probability of the end of a branch to reach the central core and the probability of contact of the ends of two branches. The size of the macromolecule, expressed by the mean square radius of gyration 〈s²〉_star is studied in the region where the interactions between the polymeric units repel one another and in the region where the units attract one another. The results are compared with the results of previous works and with experiments.     

Physico-chemical properties of whey protein isolate films containing oregano oil and their antimicrobial action against spoilage flora of fresh beef

Antimicrobial films were prepared by incorporating different levels of oregano oil (0.5%, 1.0%, and 1.5% w/w in the film forming solution) into sorbitol-plasticized whey protein isolate (WPI) films. The moisture uptake behavior and the water vapor permeability (WVP) were not affected by the addition of oregano oil at any of the concentrations used. A reduction of the glass transition temperature (∼10–20 °C), as determined by dynamic mechanical thermal analysis (DMTA), was caused by addition of oil into the protein matrix. A decrease of Young modulus (E) and maximum tensile strength (σ_max) accompanied with an increase in elongation at break (%EB) was observed with increasing oil concentration up to a level of 1.0% (w/w). Wrapping of beef cuts with the antimicrobial films resulted in smaller changes in total color difference (ΔΕ) and saturation difference (Δ_chroma) during refrigeration (5 °C, 12 days). The maximum specific growth rate (μ_max) of total flora (total viable count, TVC) and pseudomonads were significantly reduced (P < 0.05) by a factor of two with the use of antimicrobial films (1.5% w/w oil in the film forming solution), while the growth of lactic acid bacteria was completely inhibited. These results pointed to the effectiveness of oregano oil containing whey protein films to increase the shelf life of fresh beef.     

Kinetic modelling of non-enzymatic browning in honey and diluted honey systems subjected to isothermal and dynamic heating protocols

The kinetics of non-enzymatic browning (NEB) in honey and diluted honey systems was investigated. The effect of α_w (in the range of 0.54–0.99) on brown pigment formation in honey and its diluted solutions, differing in the concentration of reactant solutes was monitored upon heating at four temperatures (50, 60, 70 and 80 °C). The progression of the Maillard reaction was followed by spectrophotometric measurements at 420 nm (A₄₂₀) and the absorbance–time curves were fitted to the logistic model. The processing temperature and water activity, or the initial reactant concentration, had a significant impact on browning kinetics and the color change of honey. Secondary models, expressing the dependence of the best fitted primary model parameters on temperature and α_w, were further developed. In addition, an alternative method of expressing the temperature dependence of browning rate constants using the WLF kinetic formalism, based on the glass transition temperature, T_g, was applied. The main secondary models were validated by comparing the predicted model parameters with those obtained from isothermal experiments. Finally, the derived kinetic model was further evaluated against the observed browning responses of honey under dynamic heating conditions to examine the applicability of the developed model over fluctuating temperature–time protocols.     

Effect of the complexation with copper(II) on the hydrodynamic behaviour of some polyelectrolytes

Summary The complex formation between copper and a number of polyelectrolytes derived from amino-acids was studied by viscosimetry. It was concluded that the complexes involving two side chains of the polymer form between two neighbouring side chains of the same polymeric chain. The effect of copper on the viscosity of the polymer solutions was thus accounted for mainly by changes in the net charge of the polymer and changes in the electrostatic interactions.     

A study of steam methanol reforming in a microreactor

Steam reforming of methanol is investigated numerically considering both heat and mass transfer of the species in a packed bed microreactor. The numerical results are shown to be in good agreement with experimental data [M.T. Lee, R. Greif, C.P. Grigoropoulos, H.G. Park, F.K. Hsu, J. Power Sources Transport in, 166 (2007) 194–201] with a BASF F3-01(CuO/ZnO/Al₂O₃) catalyst. A correlation for the conversion efficiency of methanol has been obtained as a function of the operating temperature and a dimensionless time parameter which represents the ratio of the characteristic time of the methanol flow to the time for chemical reaction. The results show that for the constant wall temperature condition the steam reforming process of methanol results in a nearly uniform temperature throughout the microreactor over the range of operating conditions.     

Experimental study on spreading and evaporation of inkjet printed pico-liter droplet on a heated substrate

In this work, the spreading and evaporation of 2–70 pL droplet (17–50 μm diameter) of water and ethylene glycol jetted by drop-on-demand piezo-driven jetting head on the heated substrate are studied. According to the experimental results, the interfacial oscillation phenomena of water droplet whose Ohnesorge number (Oh) is about 10^?2 is similar to that in inviscid impact driven region, while that of ethylene glycol droplet (Oh ≈10^?1) is similar to that in highly viscous impact driven region followed by capillary driven extra spreading. In addition, various time scales used for nano/micro-liter droplets agree well with the times for interfacial oscillation, viscous damping, extra wetting, and evaporation in pico-liter droplets. In the case of water droplet, the spreading processes end before the evaporation becomes significant. However, in the case of highly viscous ethylene glycol droplet, the extra wetting overlaps the evaporation at high temperature.