Kinetic Modeling of Semi‐Interpenetrating Polymer Network (SIPN) Process ‐ A Comprehensive Study on the Case of Polyethylene/Polystyrene Semi‐I IPN

A comprehensive kinetic model is developed for a semi‐interpenetrating polymer network (SIPN) process, which involves simultaneous crosslinking, grafting, and degradation. Computational expense has been reduced considerably through a new component decomposition strategy, where a continuous variable approximation and a fixed pivot technique are applied for modeling each component. The inter‐polymer formulation is then reconstructed by a statistical approach. Based on the kinetic parameters obtained from the literature and a series of experiments, the model provides consistent agreement for gel fraction, joint molecular weight distribution (MWD) and polymer composition predicted in the studied cases, showing promising capability for the SIPN industrial application as well as for other polymer composite systems.

     

Effective spacetime and Hawking radiation from a moving domain wall in a thin film of 3He-A

An event horizon for “relativistic” fermionic quasiparticles can be constructed in a thin film of superfluid ³He-A. The quasiparticles see an effective “gravitational” field which is induced by a topological soliton of the order parameter. Within the soliton the “speed of light” crosses zero and changes sign. When the soliton moves, two planar event horizons (black hole and white hole) appear, with a curvature singularity between them. Aside from the singularity, the effective spacetime is incomplete at future and past boundaries, but the quasiparticles cannot escape there because the nonrelativistic corrections become important as the blueshift grows, yielding “superluminal” trajectories. The question of Hawking radiation from the moving soliton is discussed but not resolved. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 11, 833–838 (10 December 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Caffeine and paraxanthine HPLC assay for CYP1A2 phenotype assessment using saliva and plasma

Caffeine has been extensively used as a probe to measure CYP1A2 activity in humans with caffeine clearance or the paraxanthine (major metabolite of caffeine) to caffeine concentration ratio being regarded as the preferred metric. A simple reverse‐phased C₁₈ HPLC assay using ethyl acetate liquid–liquid extraction was developed to quantitate caffeine and paraxanthine concentrations in saliva and plasma. The mobile phase consisted of acetonitrile–acetic acid–H₂O (100:1:899) and analytes were quantitated with UV detection at 280 nm. The extraction recovery for paraxanthine and caffeine was approximately 70% in both saliva and plasma. The assay was linear over the concentration ranges 0.05–2.50 and 0.05–5.00 µg/mL, for paraxanthine and caffeine, respectively, in saliva. In plasma the assay was linear over the ranges 0.025–2.50 and 0.025–5.00 µg/mL for paraxanthine and caffeine, respectively. Intra‐ and inter‐assay precision and accuracy were less than 15%. Detection limits were 0.015 µg/mL for paraxanthine and caffeine in saliva, while it was 0.005 µg/mL for paraxanthine and caffeine in plasma. Utility was established in samples collected from two healthy volunteers who abstained from caffeine for 24 h and received a single 100 mg oral dose of caffeine. The assay developed is a robust, simple and precise technique to measure caffeine and paraxanthine in saliva and plasma of healthy volunteers after a single oral dose of caffeine. Copyright © 2010 John Wiley & Sons, Ltd.