Temporally periodic forcing

Phase separation of polystyrene/poly(vinyl methyl ether) blends was induced under spatially and temporally periodic forcing conditions by taking advantage of either photodimerization of anthracene or photoisomerization of /rt//i .9 stilbene chemically labeled on polystyrene chains. Significant mode election processes driven by these reactions were experimentally observed and analyzed for both cases. These experimental results reveal a potential method of morphology control using periodic forcing conditions. 

Phase Separation of Polymer Blends Driven by Temporally and Spatially Periodic Forcing... 

In the time or temporal domain, periodicity in operation is incorporated to realize all four principles of PI. A combination of adsorption-reaction-desorption on catalyst surface by periodic forcing of temperatures and pressures demonstrates the application of first principle. Oscillatory baffled flow reactor enhances uniformity, and illustrates the second PI principle. The application examples for third and fourth PI principles are pulsation of feed in trickle bed reactors enhancing the mass transfer rates, and flow reversal in reversed flow reactors shifting the equilibrium beyond limitations respectively. Switching from batch to continuous processing also result in realization of second and third PI principles. 

Convection in Melt Growth. Convection in the melt is pervasive in all terrestrial melt growth systems. Sources for flows include buoyancy-driven convection caused by the solute and temperature dependence of the density surface tension gradients along melt-fluid menisci forced convection introduced by the motion of solid surfaces, such as crucible and crystal rotation in the CZ and FZ systems and the motion of the melt induced by the solidification of material. These flows are important causes of the convection of heat and species and can have a dominant influence on the temperature field in the system and on solute incorporation into the crystal. Moreover, flow transitions from steady laminar, to time-periodic, chaotic, and turbulent motions cause temporal nonuniformities at the growth interface. These fluctuations in temperature and concentration can cause the melt-crystal interface to melt and resolidify and can lead to solute striations (25) and to the formation of microdefects, which will be described later. 

We present here a study on phase separation of polymer mixtures forced with temporally and spatially periodic irradiation. The main purpose is to elucidate the contribution of the elastic stress associated with the changes in polymer structure generated by chemical reactions. In the temporal modulation experiments, phase separation was induced by periodic irradiation using ultraviolet (uv) light chopped with frequency varying between 1/200 to 100 Hz. 

While other models of forced glycolysis (e.g. Richter (1984 based on the Selkov model)) demonstrates the occurrence of entrainment (the frequency locking of an autonomous oscillator by externally imposed frequencies) Hess and Markus emphasised the failure to see entrainment leading to quasi-periodic or even chaotic dynamics, and the coexistence of complicated periodic attractors. Currently the biological function of complex temporal patterns are not well-understood. Some neurobiological examples will illustrate this problem. 

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