Mixed monolayers of photoinitiatable xanthate-carrying, double-chained disulfide compound 1 and the corresponding xanthate-free compound 2 were spontaneously formed on a gold-coated quartz crystal microbalance (QCM). Self-assembling processes of these mixtures could be monitored as a frequency shift of QCM, and the composition of the resultant monolayers was found to be comparable to that of feed in solutions (f 1, mole fraction of 1 in the mixture). Photopolymerizations of methacrylic acid in aqueous solution were carried out upon UV irradiation initiated with xanthate groups of the monolayer-modified QCMs and immediately traced by measuring the frequency change. The polymerization rate was strongly dependent upon f 1 and gave a maximum at around f 1 = 0.2. In addition, the polymerization rate showed a marked pH dependence. Finally, an adsorption of cytochrome c to the poly(methacrylic acid) brushes thus prepared was examined by means of QCM and spectroscopy. As a result, cytochrome c was found to adsorb successfully to the poly(methacrylic acid) brushes through electrostatic interaction, depending upon the composition of the poly(methacrylic acid) chain grown at the monolayer surface.

Queueing network models have established their role in performance evaluation of computer systems [1]. These models have a sound theoretical background, and require less computational effort than other techniques. And they have proved to be practical in many case studies. Evaluation using simple models is powerful, especially in predicting system behaviour, and makes the internal structure of computer systems more understandable than evaluation using benchmarks. However, the modeling approach forces us to validate the model. Queueing network models are no exception to this point.