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Brain Dynamics: Neural Systems in Space and Time
Published in Ranjit Kumar Upadhyay, Satteluri R. K. Iyengar, Spatial Dynamics and Pattern Formation in Biological Populations, 2021
Ranjit Kumar Upadhyay, Satteluri R. K. Iyengar
The electric potential and concentration gradients drive the ions across the membrane channel. Potassium ions diffuse outside the cell as the external concentration of the ions is lower than the internal concentration. If we excite the cell, potassium ions carry a positive charge and flow outside the cell and leave a negative charge inside the cell. It generates outside current flow across the membrane. The positive and negative charges separate on both sides of the cell membrane which produce an electrical potential difference across the cell membrane. It is called the membrane voltage or transmembrane potential. The potential slows down the diffusion process of potassium ions as the ions are attracted to the negatively charged molecules inside the cell and they are repelled from the positively charged ions outside the cell. The concentration and electrical potential gradients apply equal and opposite forces which balance the two forces, and equilibrium is formed where the cross-membrane current becomes zero. It is denoted by the Nernst equation (see [64]): E=(RTFz)ln[[ion]outside[ion]inside],
Understanding the dynamic behavior and the effect of feeding policies of a direct contact membrane distillation for water desalination
Published in Chemical Engineering Communications, 2021
Emad Ali, Jamel Orfi, Abdullah Najib, Oualid Hamdaoui
The dynamic model is developed previously in (Ali 2019a; Ali et al. 2020) and is briefly represented here. The transient model concerns the time evolution of the MD outlet temperatures; i.e., the outlet brine temperature () and the outlet permeate temperature (). Two dynamic model structures will be considered. One structure is the lumped model which considers the entire MD module as a homogeneous system. Hence only the dynamics of the terminal temperatures () will be modeled. Another structure is the spatial model which considers the temperature variation along the MD module length, i.e., the flow direction. In this case, the model will involve the transient of the terminal as well as the internal bulk temperatures. Under each model structure, two heat transfer mechanisms will be implicated as will be described later. The following assumptions are imposed to derive the transient model for the temperatures:The thickness, tortuosity, porosity, and pore size of the membrane sheet are constant,Heat loss to the surrounding is negligible,Mass transfer by viscous flow is negligible,Cold-side channels are filled with deionized water,Equal mass flow rate on both membrane channels
Membrane separation of antibiotics predicted with the back propagation neural network
Published in Journal of Environmental Science and Health, Part A, 2023
Mixuan Ye, Haidong Zhou, Xinxuan Xu, Lidan Pang, Yunjia Xu, Jingyuan Zhang, Danyan Li
The concentration of each antibiotic in the permeate was positively correlated with the membrane pore size and negatively correlated with the running temperature and operating pressure. The running temperature and operating pressure had the greatest effects on SMZ, and the membrane pore size was correlated more strongly with the concentration of SMZ and TC in the permeate. However, the correlations of the concentration of each antibiotic in the permeate with the conductivity, salinity and pH were weak. In addition, the membrane pore size had a strong correlation with the running temperature and operating pressure. Based on the solute diffusion model, when the running temperature increased, the membrane channels became larger due to the vigorous movement of the polymer molecular chain segments, making it easier for the antibiotics in the solution to pass through. This claim was also confirmed by several investigations,[3,29,30] in which the pore size of the NF membranes used in the experiments increased by about 1.13 as the running temperature increased from 20 °C to about 45 °C. Meanwhile, it was found that there was a strong negative correlation between membrane pore size and operating pressure, and it might be caused by the actual operation. When using MF membranes, the membrane flux was already at 320 L·m−2·h−1 without turning on the lift pump, therefore, the pressure was about 1 bar, relatively low at this point. Similarly, at a pressure of about 1 bar, the membrane flux of the UF membranes was already large enough, and there was no effect on the pressure when adjusting the pressure valve. Considering the energy consumption and safety, the pressure was set to about 1 bar when using the UF membranes. The operating pressure of the NF membrane was set at 5 bar during the operation. Hence it might cause the illusion of a strong correlation between membrane pore size and operating pressure, which in turn affected the correlation between the operating pressure and the concentration of each antibiotic in the permeate. In addition, the former study of our group[26] demonstrated that pressure variation had little effect on the removal and adsorption of antibiotics by NF membranes, and only had a large effect on membrane flux. According to the above inference, the concentration of antibiotics in the permeate, the membrane pore size, operating pressure, and running temperature were mutually influenced.