• 한국광학회지
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• 제3권1호
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• pp.67-72
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• 1992

7년전 두 개의 그룹에 의해 강한 증폭된 자발 방출이 200.angs. 영역에서 관찰된 이래, 증폭도의 증가와 작동 파장영역의 확장등에서 세계적으로 많은 X-선 레이저 연구가 이루어져 왔다. X-선 레이저의 개발은 살아있는 생체조직을 고분해능으로 관찰할 수 있는 X-선 현미경 기술, 세포의 3차원 상을 가능케 하는 X-선 홀로그래피 기술, 고밀도 플라즈마의 진단 등의 여러 분야에 응용될 것이다. 국내에서도 기초적인 X-선 레이저 개발에 대한 연구가 과학기술원과 포항공과대학에서 시작되고 있어 곧 고무적인 연구결과가 나올 것으로 기대된다.

• 한국광학회:학술대회논문집
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• 한국광학회 1995년도 광학 및 양자전자학 워크샵 논문집
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• pp.185-189
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• 1995

A high-power Nb:glass laser system(Simmyung I) has been contructed and tested. In this system, we used a Nb:YLF laser as a master oscillator, a 4-pass amplifier for pre-amplification, 5 stages of rod amplifiers, and spatial filtering and image reaying usits. The system has demonstrated in excess of 80J(2TW) with 40 psec(FWHM) pulse duration. Output energy, gain and spatial were measured at each amplification stage. With this laser system a preliminary X-ray generation experiment was performed. Pinhole images, X-ray diode signals and X-ray speriment were obtained for the irradiated target of copper. Detailed descriptions of the system performance and the X-tay generation experiment are presented.

• 한국의학물리학회지:의학물리
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• 제19권3호
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• pp.150-156
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• 2008

본 연구에서는 이산 웨이브렛 도메인에서 기저계수와 웨이브렛 계수의 변환을 이용하여 X-ray 이미지의 대조도를 향상시키는 방법을 제안하였다. 기저 함수의 변환은 기존에 나와있는 contrast limited adaptive histogram equalization (CLAHE)와 multi-scale image contrast amplification (MUSICA)와 같은 보편적인 영상의 대조도 향상 기법을 적용하였으며 대조도가 향상된 저해상도 기저 계수의 역변환으로 인한 Blurring 현상을 방지하고 또한 이미지의 선명도를 향상시키기 위하여 웨이브렛 계수에 sigmoid function을 적용하였다. 본 알고리즘에 대한 성능 평가를 위하여 contrast detail mammography(CDMAM) 팬텀의 영상을 획득하여 기존에 사용한 대조도 향상 기법들과 contrast to noise ratio (CNR) 및 line profile에 대한 비교평가를 실시 하였고 그 결과 기존의 대조도 향상기법을 웨이브렛 도메인에서 적용하는 것이 뛰어나다는 것을 알 수 있었다. 본 영상 대조도 향상기법은 영상의 대조도를 증가시키는 동시에 잡음의 증폭을 효율적으로 억제할 수 있다. 따라서 본 연구는 의료 영상뿐 만이 아닌 대조도와 선명도가 중요시되는 여려 분야에 적용될 수 있으리라 기대된다.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.396-399
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• 2002

Intense quasi-monochromatic x-ray irradiation from the linear plasma target is described. The plasma x-ray generator employs a high-voltage power supply, a low-impedance coaxial transmission line, a high-voltage condenser with a capacity of about 200 nF, a turbo-molecular pump, a thyristor pulse generator as a trigger device, and a flash x-ray tube. The high-voltage main condenser is charged up to 55 kV by the power supply, and the electric charges in the condenser are discharged to the tube after triggering the cathode electrode. The x-ray tube is of a demountable triode that is connected to the turbo molecular pump with a pressure of approximately 1 mPa. As electron flows from the cathode electrode are roughly converged to the molybdenum target by the electric field in the tube, the weakly ionized plasma, which consists of metal ions and electrons, forms by the target evaporating. In the present work, the peak tube voltage was almost equal to the initial charging voltage of the main condenser, and the peak current was about 20 kA with a charging voltage of 55 kV. When the charging voltage was increased, the linear plasma x-ray source grew, and the characteristic x-ray intensities of K-series lines increased. The quite sharp lines such as hard x-ray lasers were clearly observed. The quasi-monochromatic radiography was performed by a new film-less computed radiography system.

• Journal of the Optical Society of Korea
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• 제7권3호
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• pp.135-138
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• 2003

A chirped-pulse amplification femtosecond Ti:sapphire laser operating at 1 KHz has been developed. The laser system consisted of a long-cavity femtosecond oscillator, a four-pass grating pulse stretcher, two multi-pass amplifiers and a double-pass grating pulse compressor. Thermal lensing at the amplifiers was reduced by cooling Ti:sapphire crystals using Peltier coolers. Gain narrowing and residual phase errors were compensated for by the use of an acousto-optic pulse shaper. The final laser output had an energy per pulse of 2.0 mJ and a pulse duration of 19.5 fs, reaching 0.1 TW at 1 KHz.

• 천문학회지
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• 제46권1호
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• pp.49-63
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• 2013

Nonthermal radiation from supernova remnants (SNRs) provides observational evidence and constraints on the diffusive shock acceleration (DSA) hypothesis for the origins of Galactic cosmic rays (CRs). Recently it has been recognized that a variety of plasma wave-particle interactions operate at astrophysical shocks and the detailed outcomes of DSA are governed by their complex and nonlinear interrelationships. Here we calculate the energy spectra of CR protons and electrons accelerated at Type Ia SNRs, using time-dependent, DSA simulations with phenomenological models for magnetic field amplification due to CR streaming instabilities, Alf$\acute{e}$enic drift, and free escape boundary. We show that, if scattering centers drift with the Alf$\acute{e}$en speed in the amplified magnetic fields, the CR energy spectrum is steepened and the acceleration efficiency is significantly reduced at strong CR modified SNR shocks. Even with fast Afv$\acute{e}$nic drift, DSA can still be efficient enough to develop a substantial shock precursor due to CR pressure feedback and convert about 20-30% of the SN explosion energy into CRs. Since the high energy end of the CR proton spectrum is composed of the particles that are injected in the early stages, in order to predict nonthermal emissions, especially in X-ray and ${\gamma}-ray$ bands, it is important to follow the time dependent evolution of the shock dynamics, CR injection process, magnetic field amplification, and particle escape. Thus it is crucial to understand the details of these plasma interactions associated with collisionless shocks in successful modeling of nonlinear DSA.

• 천문학논총
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• 제30권2호
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• pp.545-548
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• 2015

Most high energy cosmic rays (CRs) are thought to be produced by diffusive shock acceleration (DSA) in supernova remnants (SNRs) within the Galaxy. Plasma and MHD simulations have shown that the self-excitation of MHD waves and amplification of magnetic fields via plasma instabilities are an integral part of DSA for strong collisionless shocks. In this study we explore how plasma processes such as plasma instabilities and wave-particle interactions can affect the energy spectra of CR protons and electrons, using time-dependent DSA simulations of SNR shocks. We demonstrate that the time-dependent evolution of the shock dynamics, the self-amplified magnetic fields and $Alfv{\acute{e}nic$ drift govern the highest energy end of the CR energy spectra. As a result, the spectral cutoffs in nonthermal X-ray and ${\gamma}$-ray radiation spectra are regulated by the evolution of the highest energy particles, which are injected at the early phase of SNRs. We also find that the maximum energy of CR protons can be boosted significantly only if the scale height of the magnetic field precursor is long enough to contain the diffusion lengths of the particles of interests. Thus, detailed understandings of nonlinear wave-particle interactions and time-dependent DSA simulations are crucial for understanding the nonthermal radiation from CR acceleration sources.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.130-140
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• 2000

The earthquake hazard has been evaluated for 10km by 10km area around Kyeongju which is located near Yangsan fault and has abundant historical earthquake records. The ground motion potentials were determined based on equivalent linear analysis by using the data obtained from in situ and laboratory tests and the El centro eartqhuake record scaled to CLE and OLE of the region. The in situ tests include 9 boring investigations 2 crosshole 7 downhole 13 SASW tests and in the laboratory X-ray diffraction analyses and resonant column tests were performed. The peak ground accelerations range between 0.140g and 0.286g on CLE and between 0.051g and 0.116g on OLE respectively showing the good potential of amplification in the deep alluvial layer which is common in Kyeongju area. the response spectrum based on the Korea design guide was sometimes underestimate the motion. particularly near the natural period of the site and the importance of site-specific analysis and need for the improved site categorization method were introduced.

• Tuberculosis and Respiratory Diseases
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• 제78권2호
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• pp.64-71
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• 2015

Pulmonary tuberculosis (TB) persists as a great public health problem in Korea. Increases in the overall age of the population and the rise of drug-resistant TB have reinforced the need for rapid diagnostic improvements and new modalities to detect TB and drug-resistant TB, as well as to improve TB control. Standard guidelines and recent advances for diagnosing pulmonary TB are summarized in this article. An early and accurate diagnosis of pulmonary TB should be established using chest X-ray, sputum microscopy, culture in both liquid and solid media, and nucleic acid amplification. Chest computed tomography, histopathological examination of biopsy samples, and new molecular diagnostic tests can be used for earlier and improved diagnoses, especially in patients with smear-negative pulmonary TB or clinically-diagnosed TB and drug-resistant TB.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.390-392
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• 2005

The digital radiation detectors are used clinically by diagnostic apparatus. However the digital radiation detector are some problem like high operating voltage, light blurring, low conversion efficiency, low fill factor, etc. Thus we propose a new radiation detector that the photoconductor layer and liquid crystal layer are coupled in sandwich structure. X-ray absorption in the photoconductor layer controls the state of the liquid crystal via creation of charge carrier and the light modulation of liquid crystal make image formation. The advantage of the new radiation detector is that high resolution image is acquired and the signal amplification is possible by external visible light source. In this study, we study the optical properties and electrical properties of the new radiation detector to irradiate X-ray. The Mercury Iodide($HgI_2$) was used by photoconductor material, and the aluminum is used by reflective layer. The thickness of Mercury Iodide is about $200{\mu}m$, the operating voltage of the liquid crystal is 1.5~5V. The electrical properties of Mercury Iodide was measured, and the transmission efficiency of liquid crystal was measured by modulation potential.