This paper considers two issues arising in an integrated IEEE 802.16e/802.11 network: 1) finding a possible network, which mobile station (MSTA) can switch to, and 2) making a decision whether to execute a vertical handoff (VHO). For this purpose, we propose that 802.16e Base Stations (BSs) periodically broadcast the information about the density of 802.11 access points (APs) within their cell coverage. Based on this information, we develop a novel model, which predicts the successful scan probability during a given scan time. Using this analytical model, we devise an energy-efficient scan policy (ESP) algorithm, which enables an MSTA to decide 1) whether to attempt to discover APs in the current 802.16e cell, and 2) if so, how to set the 802.11 active scan interval considering the energy consumption. For the VHO decision, we mainly consider the impact of the service charge. Especially, a practical service fee models, i.e., flat pricing for WLAN and partially-flat pricing for 802.16e network, are considered. Under this service charge plan, we need to control the usage of the 802.16e network to minimize the user's payment. To this end, we propose a scheme, which intelligently postpones the delivery of the delay-tolerant traffic within a certain time limit combined with ESP algorithm.
Extracelluar polymeric substances (EPSs) and soluble microbial products (SMPs) produced by microbial cultures involved in membrane biofouling have been widely investigated. A mathematical model of EPS and SMP formation and degradation was established based on the activated sludge model no. 1 (ASM1) and was applied to the membrane bioreactor sludge with different sludge retention times (SRTs). The unified theory that the distinct products from the EPS and SMP overlapped each other was integrated into the ASM1. Two components, five processes and eight parameters were newly added to set up the model. To increase the accuracy of model simulation, microbial kinetic parameters were determined by respirometry method and applied to the model instead of microbial kinetic constant offered in ASM1. From the respirometry result, both of heterotroph and autotroph showed different yield value, growth rate and decay rate from activated sludge. There was no significant effect of SRT on SMP production and the experimental results showed good agreement with the predicted values by the model simulation. With the developed unified EPS and SMP model, EPS and SMP production could be simulated so well that it can be applied for the membrane biofouling control.
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