• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권9호
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• pp.3068-3086
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• 2022

Digital Forensics is gaining popularity in adjudication of criminal cases as use of electronic gadgets in committing crime has risen. Traditional approach to collecting digital evidence falls short when the disk is encrypted. Encryption keys are often stored in RAM when computer is running. An approach to acquire forensic data from RAM when the computer is shut down is proposed. The approach requires that the investigator immediately cools the RAM and transplant it into a host computer provisioned with a tool developed based on cold boot concept to acquire the RAM image. Observation of data obtained from the acquired image compared to the data loaded into memory shows the RAM chips exhibit some level of remanence which allows their content to persist after shutdown which is contrary to accepted knowledge that RAM loses its content immediately there is power cut. Results from experimental setups conducted with three different RAM chips labeled System A, B and C showed at a reduced temperature of -25C, the content suffered decay of 2.125% in 240 seconds, 0.975% in 120 seconds and 1.225% in 300 seconds respectively. Whereas at operating temperature of 25℃, there was decay of 82.33% in 60 seconds, 80.31% in 60 seconds and 95.27% in 120 seconds respectively. The content of RAM suffered significant decay within two minutes without power supply at operating temperature while at a reduced temperature less than 5% decay was observed. The findings show data can be recovered for forensic evidence even if the culprit shuts down the computer.

• 소성∙가공
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• 제3권3호
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• pp.271-281
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• 1994

Titanium-6242 $({\alpha}+{\beta})$ alloy has been used for aircraft engine components such as disks and blades, because it has an excellent strength/weight ratio at high temperatures. When this material is forged to manufacture disks, process parameters should be carefully designed to control strain and temperature distributions within the process windows by which desirable mechanical properties can be produced. In the present investigation, it was intended to design the process parameters for a conventional hot forging of this material by using a rigid-thermoviscoplastic finite element analysis technique. It was assumed that the process was performed by a screw press which is capable of maintaining a constant ram speed during loading. From the analysis results, it was found out that the initial temperature of the workpiece and the die shape were important parameters to control the forging process. In result, these parameters were properly designed for hot forging of a disk with specific dimensions.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2012년도 춘계학술발표회 논문집
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• pp.238-239
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• 2012

ZnO disk는 Ar 가스의 ON/OFF 사이클을 사용한 기상 이동법으로 성장하였다. 온도 의존성 photoluminescence (PL)은 PL 스펙트럼의 quenching 동작을 관장하는 메커니즘을 연구하기 위해 조사하였다. ZnO disk의 12 K PL 스펙트럼에서 3.364, 3.315, 3.244, 3.212, 3.170, 3.139, 3.100 eV의 피크를 관측되었고, 그것은 각각 excitons bound to neutral donors ($D^{\circ}X$), A-line, first-order longitudinal optical (1LO) phonon replica of A-line (A-1LO), donor-to acceptor pair (DAP), A-2LO, DAP-1LO, A-3LO 이다. $D^{\circ}X$와 A-line 피크는 Varshni 공식에 의해서 피팅을 하였고, 도너 이온화 에너지는 40 meV 이었다. Free excitons, $D^{\circ}X$, A-line의 lifetime은 이론적으로 계산하였고, 온도가 증가함에 따라 lifetime이 증가하였다.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2009년도 추계학술발표대회
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• pp.247-248
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• 2009

램 디스크는 주기억장치의 일부 영역을 스토리지로 이용하는 디스크 시스템이다. 램 디스크는 반도체 메모리에 데이터를 저장하고 접근하기 때문에 디스크 입출력 성능은 매우 높다. 그러나, 휘발성 메모리를 이용하는 램 디스크는 전원 공급이 중단되면 그 저장 내용이 소실되는 단점을 가지고 있다. 본 논문에서는 리눅스 장치 구동기 수준에서 램 디스크 서비스와 동시에 하드 디스크 등의 비휘발성 저장 장치에 데이터를 저장, 서비스하는 하이브리드 디스크 시스템을 제안한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 B
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• pp.1009-1012
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• 1999

Recently, there is a strong need of DVD (Digital Versatile Disk) system of high density. high speed, and high accuracy System performances mostly depend on not only optical system, but also servo technology to drive it. Therefore, we investigate main technology concerned with optical pick-up unit based on 4.7GB DVD-RAM and analyzes technology of optical and servo systems that are required for high density high speed and high accuracy from the viewpoint of control. And then, we design a linear controller based on specification of 4.7GB DVD-RAM that is commercially available now. We analyze the dynamic characteristics of optical system that is coupled with control system and verify effect on performance indices of servo due to Parameter variation of pick-up by simulation. Finally, we will propose controller design specifications and provide direction of technical development for servo system and problems coupled with high capacity for 15GB level in the future.

• 천문학회보
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• 제36권2호
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• pp.117.2-117.2
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• 2011

We probe 12CO J=2-1 and 13CO J=1-0 properties of a Virgo disk galaxy, NGC 4402 which is located near the cluster center. Our goal is to study the impact of intra cluster medium (ICM) on the molecular gas of a galaxy in the cluster environment. It has been believed that cluster galaxies are deficient in atomic hydrogen gas (HI gas) compared to their field counterparts and now there is much evidence that low density ISM can be easily removed by ram pressure caused by ICM wind. Meanwhile, no significant molecular gas deficiency of the cluster galaxy population has been found yet they show overall lower star formation rate than galaxies in the field, and it is still controversy whether dense ISM can be also stripped by the ICM wind or not. NGC 4402 with truncated HI disk($D_{HI}/D_{opt}$ ~ 0.75 and only 36%of HI gas compare to field galaxies of a similar size) and a disturbed gas morphology, appears to have strong ongoing ram pressure. Using high resolution 12 and 13CO data of NGC 4402 from a Sub Millimeter Array (SMA), we probe the molecular gas properties under strong ICM pressure. We discuss how its star formation activity and hence the global color of NGC4402 would be changed in the future.

• 한국정보과학회논문지:시스템및이론
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• 제30권5_6호
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• pp.232-238
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• 2003

기존 운영체제들은 물리적 메모리보다 더 많은 양의 메모리를 사용자에게 제공하기 위하여 가상 메모리 페이징 시스템을 사용한다. 가상 메모리 페이징 시스템에서는 물리적 메모리가 부족해지면 교체되는 메모리 내용을 저장시킬 수 있는 스왑 장치를 필요로 하는데, 기존 운영 체제들에서는 디스크를 스왑 장치로 사용한다. 디스크는 물리적 메모리에 비해 접근 속도가 매우 느리기 때문에 스왑핑이 일어나면 물리적 메모리의 접근 시간에 비해 많은 시간을 기다려야 한다. 여러 대의 PC를 빠른 네트웍으로 묶는 클러스터 환경에서는 디스크의 접근 시간보다 네트웍을 통하여 다른 워크스테이션의 메모리에 접근하는 시간이 더 빠르기 때문에 사용 가능한 다른 워크스테이션의 메모리를 디스크 대신 빠른 장치로 사용하고자 하는 네트웍 램이 제시되었다. 본 논문에서는 Linux 운영 체제에서 스왑 장치 관리자로 네트웍 램을 설계, 구현하여 디스크를 스왑 장치로 사용하는 시스템보다 네트웍 램을 스왑 장치로 사용하는 시스템이 프로그램 수행 속도에 있어 평균 40.3%의 성능 향상이 있었다. 그리고 기존 RAID 시스템에서 사용하던 안정성 제공 방법과 다른 프로세서의 성능을 효율적으로 이용하는 새로운 안정성 제공방법을 제시하였고 평가 결과 본 논문에서 제시한 새로운 안정성 제공 방법인 압축을 이용한 복사본을 두는 방법은 적은 서버 메모리와 메시지를 사용하여 유사한 성능을 나타낸다.

• 천문학회보
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• 제42권2호
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• pp.75.1-75.1
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• 2017

Ram pressure due to the intracluster medium (ICM) is known to play a crucial role in removing the cool gas content of a galaxy on a short timescale, potentially driving a star forming galaxy to evolve into a red passive population. Although many HI imaging studies find clear evidence of diffuse atomic gas stripping from cluster galaxies, it is still debatable whether the ram pressure can also strip dense molecular gas. NGC 4522, a Virgo spiral, undergoing strong ram pressure stripping, is one of the few cases where extraplanar CO emission together with stripped HI gas and $H{\alpha}$ knots has been identified, providing an ideal laboratory to study the molecular gas stripping event and the extraplanar star formation activity. The aim of this work is to investigate the origin of extraplanar molecular clouds near NGC 4522 (e.g. stripped or forming in situ), and to probe a relation between the molecular gas surface density and the star formation rate (i.e. the Kennicutt-Schmidt law) at sub-kpc scale, especially in the extraplanar space, using ALMA Cycle 3 CO data and $H{\alpha}$ data of NGC 4522. We present the results from our ALMA observations, and discuss possible scenarios for the origin of extraplanar molecular clouds and to characterize the star formation activity associated with stripped gas outside the galactic disk.

• 천문학회보
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• 제43권1호
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• pp.62.1-62.1
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• 2018

Galaxies in the cluster environment interact with the intracluster medium (ICM), losing the interstellar medium (ISM) and alternating their evolution. Observational evidences of the extraplanar ISM stripped by the ICM's ram pressure are prevalent in HI imaging studies of cluster galaxies. However, current theoretical understanding of the ram pressure stripping (or ICM-ISM interaction in general) is still limited mainly due to the lack of numerical resolution at ISM scales in large-scale simulations. Especially, self-consistent modeling of the turbulent, multiphase ISM is critical to understand star formation in galaxies interacting with the ICM. To achieve this goal, we utilize the TIGRESS simulation suite, simulating a local patch of galactic disks with high resolution to resolve key physical processes in the ISM, including cooling/heating, self-gravity, MHD, star formation, and supernova feedback. We then expose the ISM disk to ICM flows and investigate the evolution of star formation rate and the properties of the ISM. By exploring ICM parameter space, we discuss an implication of the simple ram pressure stripping condition (so called the Gunn-Gott condition) to the realistic ISM.

• 전자공학회논문지CI
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• 제38권4호
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• pp.33-38
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• 2001

고밀도 기록매체인 DVD RAM 시스템에서 단면 기록밀도 4.7 GB, 15 GB 매체 개발 실현에 가장 큰 걸림돌로 작용하고 있는 crosserase 및 crosstalk 현상이 재생 신호에 미치는 영향을 분석하기 위해 4.7 GB 및 15 GB 규격으로 재생 신호를 시뮬레이션 하였다. 디스크에 조사된 빔의 강도는 Gaussian으로 근사화하고 기록된 마크는 타원형 마크로 가정하였으며, 재생신호는 Gaussian 빔 패턴과 마크 패턴의 이중 적분으로 계산되었다. Crosserase 정도를 변하여 얻어진 재생 신호로부터 주파수 분석을 통하여 3T-11T 마크의 carrier level의 크기를 구하여 비교하였다. 1,000개의 3T-11T 랜덤 마크로 부터 crosserase 및 crosstalk 에 의한 지터를 계산하여 비교한 결과, crosserase에 의한 지터가 crosstalk에 의한 지터 보다 상대적으로 작음을 확인할 수 있었다.