Gyujin Kim

DNA damage and mitochondria dysfunction in cell apoptosis induced by nonthermal air plasma

Nonthermal plasma is known to induce animal cell death but the mechanism is not yet clear. Here, cellular and biochemical regulation of cell apoptosis is demonstrated for plasma treated cells. Surface type nonthermal air plasma triggered apoptosis of B16F10 mouse melanoma cancer cells causing DNA damage and mitochondria dysfunction. Plasma treatment activated caspase-3, apoptosis executioner. The plasma treated cells also accumulated gamma-H2A.X, marker for DNA double strand breaks, and p53 tumor suppressor gene as a response to DNA damage. Interestingly, cytochrome C was released from mitochondria and its membrane potential was changed significantly.

Comparison between particle-in-cell Monte-Carlo and fluid simulations of argon microhollow discharges

In this study, Particle-in-cell Monte-Carlo (PIC-MCC) and fluid simulations of Argon Microhollow cathode discharges with cylindrical cathode and planar anode are presented. The simulation conditions of two codes are same: the longest gap distance between top cathode and bottom anode, d , is 200 μm and cathode hole diameter, D, is 100 μm [1], and a pressure is at 100 Torr. However, PIC simulations are driven by 10 mA dc current while fluid simulations are driven by 200 V dc voltage. Fig. 1 shows rather different electron density profiles each other, but the peak value is the same order. The peak densities are about 1.2 × 1022 m−3 and 2.0 × 1022 m−3, and the plasma potential values are about 140 and 200 V for PIC and fluid simulation, respectively. Fig. 1 also represents that the discharges of simulations are developed in the hole of cathode [2]. In the case of relatively low pressure (10 Torr) discharge, however, a discharge of fluid simulation is extinguished although PIC simulation has the electron density profile similar to the 100 Torr case. This difference is due to different boundary conditions of fixed current and voltage. The our fluid code has not been working by current driven source, while the our PIC code has done by both sources. Because our group was already doing the PIC simulation, which needs a long period time in order to obtain one result, using fixed current source, the comparison by different condition was carried out. As further simulations with two codes are carried out using same boundary conditions of voltage, more precise comparisons under various pressures would come to be obtained.

Coherent synchrotron radiation monitor for microbunching instability in XFEL

The microbunching instability is an important issue in an X-ray Free Electron Laser (XFEL). The intensity of the Free Electron Laser (FEL) can be reduced significantly by the microbunching instability so that the laser heater is widely used to reduce it. In the X-ray Free Electron Laser of the Pohang Accelerator Laboratory (PAL-XFEL), to directly monitor the microbunching instability, a visible charge coupled device camera was included into the coherent radiation monitor which uses a pyroelectric detector. It enabled us to measure the microbunching instability more clearly and optimize the FEL lasing in the PAL-XFEL.

Soft X-ray harmonic lasing self-seeded free electron laser at Pohang Accelerator Laboratory X-ray free electron laser

The demonstration of a harmonic lasing self-seeded free-electron laser (HLSS FEL) scheme in the soft X-ray range at the Pohang Accelerator Laboratory X-ray Free Electron Laser is presented. We report the experimental results of HLSS FEL radiation with the shortest wavelength of 1 nm by using the optimized phase shift of 2/3π. The key feature of the HLSS scheme is that the mode number is decreased (the longitudinal coherence length is enhanced) which is directly observed using a single-shot spectrometer. The spectral brightness is enhanced by a factor of 1.7 compared to the self-amplified spontaneous emission FEL because of the narrowed bandwidth. Our results show a good agreement with the theoretical expectation and simulations. The HLSS mode is a promising standard operation mode to generate a stable and high-brightness X-ray FEL that will provide more benefits to users for various applications.The demonstration of a harmonic lasing self-seeded free-electron laser (HLSS FEL) scheme in the soft X-ray range at the Pohang Accelerator Laboratory X-ray Free Electron Laser is presented. We report the experimental results of HLSS FEL radiation with the shortest wavelength of 1 nm by using the optimized phase shift of 2/3π. The key feature of the HLSS scheme is that the mode number is decreased (the longitudinal coherence length is enhanced) which is directly observed using a single-shot spectrometer. The spectral brightness is enhanced by a factor of 1.7 compared to the self-amplified spontaneous emission FEL because of the narrowed bandwidth. Our results show a good agreement with the theoretical expectation and simulations. The HLSS mode is a promising standard operation mode to generate a stable and high-brightness X-ray FEL that will provide more benefits to users for various applications.