Condensed-mode operation of an ethylene polymerization fluidized-bed reactor is of great significance in academic and industrial circles. Based on the classical emulsion–bubble two-phase model, this article proposes an FBR model for condensed-mode operation by taking into consideration the addition of a condensed liquid and its evaporation. In this model, two different flow regimes, the gas–liquid–solid (G–L–S) and gas–solid (G–S) zones, are assumed to coexist in one FBR. Moreover, the emulsion phase in the FBR is regarded as being in plug flow in the G–L–S zone and in well-mixed flow in the G–S zone, whereas the bubble phase is always treated as being in plug flow throughout the whole FBR. Modeling of the temperatures of the emulsion and bubble phases allows the temperature profile of the ethylene polymerization FBR to be obtained. The simulation results show that the bed temperature rises sharply in the G–L–S zone above the gas distributor and then remains nearly constant in the G–S zone. Moreover, the G–L–S zone gradually expands upward with a corresponding increase in condensed liquid in the recycling stream. The simulated results compare fairly well with those from an industrial FBR unit. Based on the proposed model, the effects of bubble size on heat transfer and bed temperature profile were also studied.

The adsorption and aggregation of the amyloid-beta (Abeta) peptides on the cell membrane plays a causal role in the pathogenesis of Alzheimer's disease. Here, we report all-atom molecular dynamics (MD) simulations to study the interactions of Abeta oligomer with self-assembled monolayers (SAMs) terminated with hydrophobic CH(3) and hydrophilic OH functional groups, with particular interests in how surface chemistry and Abeta orientation affect the adsorption behavior of Abeta. Simulation results show that the CH(3)-SAM has a stronger binding affinity to Abeta than the OH-SAM does, although both surfaces can induce Abeta adsorption. Regardless of the characteristics of the surface, the hydrophobic C-terminal region is more likely to be adsorbed on the SAMs, indicating a preferential orientation and interface for Abeta adsorption. Structural and energetic comparison among six Abeta-SAM systems further reveals that Abeta orientation, SAM surface hydrophobicity, and interfacial waters all determine Abeta adsorption behavior on the surface, highlighting the importance of hydrophobic interactions at the interface. This work may provide parallel insights into the interactions of Abeta with lipid bilayers.

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