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  1. The dynamics of a soft particle suspended in a viscous fluid can be changed by the presence of an elastic boundary. Understanding the mechanisms and dynamics of soft–soft surface interactions can provide valuable insights into many important research fields, including biomedical engineering, soft robotics development, and materials science. This work investigates the anomalous transport properties of a soft nanoparticle near a visco-elastic interface, where the particle consists of a polymer assembly in the form of a micelle and the interface is represented by a lipid bilayer membrane. Mesoscopic simulations using a dissipative particle dynamics model are performed to examine the impact of micelle’s proximity to the membrane on its Brownian motion. Two different sizes are considered, which correspond to ≈10−20nm in physical units. The wavelengths typically seen by the largest micelle fall within the range of wavenumbers where the Helfrich model captures fairly well the bilayer mechanical properties. Several independent simulations allowed us to compute the micelle trajectories during an observation time smaller than the diffusive time scale (whose order of magnitude is similar to the membrane relaxation time of the largest wavelengths), this time scale being hardly accessible by experiments. From the probability density function of the micelle normal position with respect to the membrane, it is observed that the position remains close to the starting position during ≈0.05τd (where τd corresponds to the diffusion time), which allowed us to compare the negative excess of mean-square displacement (MSD) to existing theories. In that time range, the MSD exhibits different behaviors along parallel and perpendicular directions. When the micelle is sufficiently close to the bilayer (its initial distance from the bilayer equals approximately twice its gyration radius), the micelle motion becomes quickly subdiffusive in the normal direction. Moreover, the temporal evolution of the micelle MSD excess in the perpendicular direction follows that of a nanoparticle near an elastic membrane. However, in the parallel direction, the MSD excess is rather similar to that of a nanoparticle near a liquid interface.

     
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    Free, publicly-accessible full text available December 28, 2024
  2. Distributed optimization is becoming popular to solve a large power system problem with the objective of reducing computational complexity. To this end, the convergence performance of distributed optimization plays an important role to solve an optimal power flow (OPF) problem. One of the critical factors that have a significant impact on the convergence performance is the reference bus location. Since selecting the reference bus location does not affect the result of centralized DC OPF, we can change the location of the reference bus to get more accurate results in distributed optimization. In this paper, our goal is to provide some insights into how to select reference bus location to have a better convergence performance. We modeled the power grid as a graph and based on some graph theory concepts, for each bus in the grid a score is assigned, and then we cluster buses to find out which buses are more suitable to be considered as the reference bus. We implement the analytical target cascading (ATC) on the IEEE 48-bus system to solve a DC OPF problem. The results show that by selecting a proper reference bus, we obtained more accurate results with an excellent convergence rate while improper selection may take much more iterations to converge. 
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