Image quality as a function of unsharp masking band center

Unsharp masking is an image enhancement technique used to obtain a Modulation Transfer Function (MTF) greater than unity within a given spatial frequency band. In unsharp masking, the mask forms a slightly blurred version of the original image. The result is more severe in the high frequency region than at low frequencies. The final image is made by combining the original positive and the blurred negative images. The subjective quality of images resulting from unsharp masking is a function of the frequency response of the human eye. This study evaluates the unsharp masking technique by implementing the Subjective Quality Factor (SQF) criterion

Lattice Boltzmann simulation of liquid water transport in gas diffusion layers of proton exchange membrane fuel cells: Parametric studies on capillary hysteresis

Water management is crucial for reliable operation of Polymer Electrolyte Membrane Fuel Cells (PEMFC). Here, the gas diffusion layer (GDL) plays an essential role as it has to ensure efficient water removal from and oxygen transport to the catalyst layer. In this study water transport through porous carbon felt GDLs was simulated using a 3D Color-Gradient Lattice Boltzmann model. Simulations were carried out on microstructures of plain and impregnated fiber substrates of a Freudenberg H14. The GDL microstructures were reconstructed from high-resolution X-ray micro-computed tomography ($\mu$-CT). For the distinction of carbon fibers and polytetrafluoroethylene (PTFE) in the binarized microstructures an in-house algorithm was developed. The additive was specified heterogeneously in the GDL through-plane direction employing a PTFE loading profile as derived based on $\mu$-CT image data. In the in-plane direction the additive was furthermore defined in a realistic fashion near carbon fiber intersections. Prior to parametric studies on capillary behavior a sophisticated modeling approach for semipermeable membranes had to be developed to account for experimental boundary conditions. Capillary hysteresis was then investigated by simulation of intrusion and drainage curves and subsequent comparison to testbench data