Youngbin Cho

Homogenizing cellular tension by hepatocyte growth factor in expanding epithelial monolayer

Hepatocyte growth factor (HGF) induces cell migration and scattering by mechanisms that are thought to tip a local balance of competing physical forces; cell-to-cell and cell-to-substrate forces. In this local process, HGF is known to attenuate local cadherin-dependent adhesion forces for cell-cell junction development and enhance local integrin-dependent contractile forces for pulling neighboring cells apart. Here we use an expanding island of confluent Madin-Darby canine kidney (MDCK) cells as a model system to quantify the collective cell migration. In the absence of HGF, cell trajectories are highly tortuous whereas in the presence of HGF, they become far less so, resembling free expansion of a gas. At the level of cell-to-cell junctions, HGF attenuates the linkage of stress fibers to cell-to-cell junctions with concomitant decrease in intercellular stress. At the level of cell-to-substrate junctions, HGF augments the linkage of stress fibers to cell-to-substrate junctions with no apparent effect on traction. Together, HGF induces both structural changes in the actin-bound junctional protein complex and physical forces spanning multicellular clusters, which further promotes the expansion of confluent cellular layer.

A new method for image separation of overlapped images from a two-layered printed circuit board (PCB)

Abstract Conventional laminography provides cross-sectional X-ray imaging which separates the top and bottom sides, or any other layer of the printed circuit board (PCB), into separated images. However, only an image on the focal plane is obtained by a set of projections. Furthermore, the image is blurred by superimpositions of the out-of-focus structures. This paper presents a new method for image separation via object translation with a moving X-Y table instead of synchronously rotating or translating two components, i.e. a source and detector. This method uses a recursive process with a simple mathematical function which is derived analytically by the X-ray projection geometry. An X-ray imaging system has been constructed for the purpose of evaluating the proposed method, and was used for the test sample experiments. The experimental results confirm that the method is a powerful tool for separating objects from overlapped X-ray images.

Development of axial laminographic system for electronic packaging inspection

X‐ray laminographic image can provide more useful information about the internal state of electronic packaging than x‐ray radiographic image does. Many kinds of laminographic system have been developed for obtaining the cross‐sectional image. Proposes an axial laminographic system, which can be constructed by usual automatic radiographic system without any rotating x‐ray head and detector system. Explains that this method can be implemented to make the usual radiographic x‐ray inspection system equal to the power of a laminographic system.