• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.33.1-33.1
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• 2018

Ram pressure stripping by intracluster medium (ICM) can play a crucial role in galaxy evolution in the high-density environment as seen by many examples of cluster galaxies. Although much progress has been made by direct numerical simulations of galaxies (or a galaxy) as a whole in a cluster environment, the interstellar medium (ISM) in galactic disks is not well resolved to understand responses of the ISM in details. In order to overcome this, we utilize the TIGRESS simulation suite that focuses on a local region of galactic disks and resolves key physical processes in the ISM with uniformly high resolution. In this talk, we present the results from the solar neighborhood TIGRESS model facing the ICM winds with a range of ram pressures. When ram pressure is weaker than and comparable to the ISM weight, the ICM winds simply reshape the ISM to the one-sided disk, but star formation rates remain unchanged. Although there exist low-density channels in the multiphase ISM that allow the ICM winds to penetrate through, the ISM turbulence quickly closes the channels and prevents efficient stripping. When ram pressure is stronger than the ISM weight, a significant amount of the ISM can be stripped away rapidly, and star formation is quickly quenched. While the low-density gas is stripped rapidly, star formation still occurs in the extraplanar dense ISM (1-2kpc away from the stellar disk). Finally, we quantify the momentum transfer from the ICM to the ISM using the mass-and momentum-weighted velocity distribution functions of each gas phase.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.54.1-54.1
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• 2018

Recent observational studies suggest that the environmental effects can shape the evolution of galaxies in clusters. In an attempt to better understand this process, we perform idealized radiation-hydrodynamic simulations of RAM pressure stripping on star-forming galaxies using RAMSES-RT. We find that extended HI disks are easily stripped by moderate ICM winds, while there is no significant decrease in the total mass of molecular gas. RAM pressure tends to compress the molecular gas, leading to enhanced star formation especially when the gaseous disk is hit by edge-on winds. On the other hand, strong ICM winds that are expected to operate at the centre of clusters strip both HI and molecular gas from the galaxy. Interestingly, we find that the strong ICM winds can induce the formation of relatively dense (~1H/cc) HI gas clouds at a distance from the disk.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.432-437
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• 2001

It is necessary to improve mechanical and optical porperties in the optical disk substrates as the information storage devices with high storage density using blue laser are being developed. Injection compression molding is regarded as the most suitable process to manufacture optical disk substrates for quality recording and read-out. In the present research, the effects of processing conditions and the insulation layer thickness on gapwise birefringence and the land-groove pattern were investigated. It was found that the values of the birefringence distribution were very sensitive to mold temperature history, and the level of birefringence reduced and, furthermore, the quality of replication was improved due to the insulation layer.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.11a
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• pp.1591-1594
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• 2010

NAND 플래시 메모리 기반의 Solid State Disk (SSD)의 내부에는 Flash Translation Layer (FTL)이라는 소프트웨어가 사용되고 있다. FTL은 파일 시스템으로부터 요청되는 논리 주소를 플래시 메모리의 물리 주소로 변환하며 이를 위하여 사상 테이블을 사용한다. 사상 테이블의 빠른 접근을 위하여 사상 테이블은 SSD 내부의 RAM에 유지하는데 SSD의 용량이 커지게 되면 사상 테이블로 인해 요구되는 RAM의 크기도 커지는 문제점이 있다. 본 논문에서는 FTL의 사상 테이블을 페이지 단위로 나누어 필요할 때마다 RAM에 적재하는 다단계 사상 테이블 기법을 연구하였다.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.61.3-62
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• 2016

NGC 4522 is a spiral galaxy located in the Virgo cluster which appears to be undergoing active ram pressure stripping due to the intracluster medium (ICM). What makes this galaxy special is the extraplanar CO gas, some of which coincides with the extraplanar $H{\alpha}$ patches. As one of the few cases where the interstellar molecular gas is thought to have been pushed out from the stellar disk by the ICM, this galaxy provides an opportunity to study the impact of ICM pressure on the dense/star forming gas and its fate in the extraplanar space after stripping. In order to probe detailed molecular gas properties inside and outside the stellar disk and the associated star formation activities, we have observed NGC 4522 in 12CO (1-0) and 13CO (1-0) using the ALMA. We have targeted two regions, one around the center of the galaxy and one centered on the peak of the extraplanar CO, detecting both lines in both regions. Particularly, this is the first case where 13CO gas has been detected outside the stellar disk in a galaxy undergoing ram pressure stripping. In this work, we present preliminary results from the ALMA observations and discuss the evolution of molecular gas properties and star formation activities inside and outside the stellar disk.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.5
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• pp.537-541
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• 2008

Log-Structured File System(LFS) is a disk based file system that is optimized for improving the write performance. LFS gathers dirty data in memory as long as possible, and flushes all dirty data sequentially at once. In a real system, however, maintaining dirty data in memory should be flushed into a disk to meet file system consistency issues even if more memory is still available. This synchronizations increase the cleaner overhead of LFS and make LFS to write down more metadata into a disk. In this paper, by adapting Non-volatile RAM(NV-RAM) we modifies LFS and virtual memory subsystem to guarantee that LFS could gather enough dirty data in the memory and reduce small disk writes. By doing so, we improves the performance of LFS by around 2.5 times than the original LFS.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.47 no.5
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• pp.35-40
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• 2010

NAND flash memory has been widely used than traditional HDD in PDA and other mobile devices, embedded systems, PC because of faster access speed, low power consumption, vibration resistance and other benefits. DiskSim and other HDD simulators has been developed that for find improvements for the software or hardware. But there is a few Linux-based simulators for NAND flash memory and SSD. There is necessary for Windows-based NAND flash simulator because storage devices and PC using Windows. This paper describe for development of simulator-NFSim for FTL performance analysis in NAND flash. NFSim is used to measure performance of various FTL algorithms and FTL wear-level. NAND flash memory model and FTL algorithm developed using Windows Driver Model and class for scalability. There is no need for another tools because NFSim using graph tool for data measure of FTL performance.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.438-444
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• 2001

The objective of this study is to provide a simple methodology to find optimum processing conditions to fabricate sub-micron structured DVD-RAM substrates with superb optical and geometrical properties. It was found that the birefringence, which is regarded as one of the most important optical properties for an optical disk, was very sensitive to the mold wall temperature history. Also, the integrity of the replication, represented by the land-groove structure and the radial tilt were influenced by the mold temperature and the compression pressure. A set of optimum conditions were obtained by applying Design of Experiment and the objective functions composed of three different objectives.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.65.1-65.1
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• 2020

We present high-resolution, high-sensitivity continuum data of NGC 4522 observed at 3 cm (X-band) and 10 cm (S-band) in full polarization mode using the JVLA. This observation has 2 - 4 times better spatial resolution and 2 - 5 times better sensitivity compared to previous continuum observations. NGC 4522 is a Virgo spiral galaxy undergoing active ram pressure stripping. This galaxy is particularly well known for the CO emission detected outside its stellar disk, some of which coincides with the extraplanar HI gas and Halpha patches. The major goal of our JVLA observation is to leverage our understanding of the influence of the ram pressure on the general ISM field and multi-phase medium. By combining our new deep radio continuum data and previous observations, we will investigate how the B-field properties can be affected by the ram pressure, and what roles the B-field plays in the stripping process of the multi-phased ISM and in the star formation activity when the ram pressure is present.

• Proceedings of the Korea Information Processing Society Conference
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• 2001.10a
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• pp.283-286
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• 2001

전통의 자기 디스크 형태 저장 장치로의 접근 지연 시간을 줄이고자, 최근에 서로 네트워크로 연결된 컴퓨터간의 메모리 자원들을 파일을 저장하는 장치로써 활용해 볼 수 있는 가상 장치(Network RamDisk)가 개발되었다. 이 시스템은 메모리 공간을 제공해 주는 서버의 노드들이 패리티 그룹(parity group)을 이루는 일종의 software RAID 시스템으로 한 서버의 노드 crash 에 대해 대응하는 것을 고려하지 않아 제 이의 서버가 노드 crash, 프로세스 crash 혹은 데이터 손실을 발생시키면 완전히 데이터를 잃어버리는, 신뢰성이 낮은 문제점이 있다. 본 논문은 클라이언트가 서버측의 노드 crash를 적절히 감지하고 새로운 서버로 fail over 할 수 있는 여러 가지 기법들을 설계하고 구현하였다. 또한 서버 풀(server pool)이라는 가상의 공간을 따로 관리하여 서버들에 대한 메모리 자원 요구 부하를 균등히 분산 시키는 효과도 얻도록 하였다.