• Communications of the Korean Mathematical Society
• /
• v.21 no.3
• /
• pp.409-417
• /
• 2006

자연현상의 복잡한 대상의 연구에서 출발한 프랙탈의 연구는 물리학에서 특히 열역학에서의 기법을 활용한 다중프랙탈의 연구로까지 그 영역이 확대되었다. 이 논문에서는 프랙탈과 다중프랙탈의 여러 가지 성질과 그 응용에 대한 최근 결과를 소개한다

• Korean Journal of Optics and Photonics
• /
• v.33 no.6
• /
• pp.252-259
• /
• 2022

We have conducted a study to control the light-intensity distribution at the output end of a multimode optical fiber via estimating the transmission matrix. A circularly arranged Hadamard eigenmode phase distribution was implemented using a spatial light modulator, and the transmission matrix of a multimode optical fiber was experimentally obtained using a four-phase method. Based on the derived transmission matrix, the spatial phase distribution of light incident upon the optical fiber was adjusted via the spatial light modulator in advance, to focus the light at a desired position at the optical fiber output. The light could be focused with an intensity up to 359.6 times as high as that of the surrounding background signal at a specific position of the multimode fiber's output end, and the intensity of the focused beam was on average 104.6 times as large as that of the background signal, across the area of the multimode fiber's core.

• New Physics: Sae Mulli
• /
• v.68 no.11
• /
• pp.1167-1172
• /
• 2018

Carbon nanotubes (CNTs) are structures of carbon atoms bonded together in hexagonal honeycomb shapes, with multi-walled CNTs having a very high thermal conductivity of $3000W/m{\cdot}K$ and single-walled CNTs having a conductivity of $6000W/m{\cdot}K$. In this work, the transmittance and the thermal diffusivity of a multi-walled carbon nanotube dispersion with a concentration of 1.5 M were measured using a single beam method, a dual beam method, and the thermal lens effect. The nonlinear optical coefficients were obtained by using the z-scan method, which moved the sample in the direction of propagation of the single laser beam, propagation and the thermal diffusivity was measured using a double laser beam. As a pump beam, a diode-pumped solid state (DPSS) laser with a wavelength of 532 nm and an intensity of 100 mW was used. As the probe beam, a He-Ne laser having a wavelength of 633 nm and an intensity of 5 mW was used. The experimental result shows that when the concentrations of the sample were 9.99, 11.10, 16.65, and 19.98 mM, the nonlinear absorption coefficients were 0.046, 0.051, 0.136 and 0.169 m/W, respectively. Also, the nonlinear refractive indices were 0.20, 0.51, 1.25 and $1.32{\times}10^{-11}m^2/W$, respectively, and the average thermal diffusivity was $1.33{\times}10^{-6}m^2/s$.

• Progress in Medical Physics
• /
• v.26 no.1
• /
• pp.18-27
• /
• 2015

Since a Compton camera has high detection sensitivity due to electronic collimation and a good energy resolution, it is a potential imaging system for nuclear medicine. In this study, we investigated the feasibility of a Compton camera for multi-tracer imaging and proposed a rotating Compton camera to satisfy Orlov's condition for 3D imaging. Two software phantoms of 140 and 511 keV radiation sources were used for Monte-Carlo simulation and then the simulation data were reconstructed by listmode ordered subset expectation maximization to evaluate the capability of multi-tracer imaging in a Compton camera. And the Compton camera rotating around the object was proposed and tested with different rotation angle steps for improving the limited coverage of the fixed conventional Compton camera over the field-of-view in terms of histogram of angles in spherical coordinates. The simulation data showed the separate 140 and 511 keV images from simultaneous multi-tracer detection in both 2D and 3D imaging and the number of valid projection lines on the conical surfaces was inversely proportional to the decrease of rotation angle. Considering computation load and proper number of projection lines on the conical surface, the rotation angle of 30 degree was sufficient for 3D imaging of the Compton camera in terms of 26 min of computation time and 5 million of detected event number and the increased detection time can be solved with multiple Compton camera system. The Compton camera proposed in this study can be effective system for multi-tracer imaging and is a potential system for development of various disease diagnosis and therapy approaches.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2006.11a
• /
• pp.299-302
• /
• 2006

We present an innovative means of numerically treating interfaces associated with chemically active energetic materials. Recent advances in wave tracking technique based on the Ghost Fluid Concept is extended to handle multi-material multi-phase interfaces associated with chemical environment associated with explosion. We show several work-in-progress applications of our code, including the impact problems involving both energetic and inert elements. Accurate modeling of the equation of state and the constitutive relations are also discussed

• Tribology and Lubricants
• /
• v.13 no.2
• /
• pp.1-7
• /
• 1997

나는 12월의 첫째주를 두려워 했다. 그것은 나를 우울하게 하는 보스턴의 진눈깨비 섞인 이슬비나 어둠, 그리고 붐비는 휴일의 쇼핑몰의 주차전쟁같은 것은 아니었다. 그 주가 응축 물질 연구 물리학자들의 모임인 미국물리학회의 3월 총회에 제출할 논문 초록의 마감 시한이기 때문이다. 1986년에 나는 나의 대학 동료 Allan Widom과 함께 고체 평면을 따라서 미끄러지는 한 원자 두께 필름의 마찰력을 측정할 수 있는 실험 기술을 개발했다. 문제는 나의 원자단위의 마찰 초록을 3월 총회의 수많은 논문들 중 어디에 분류해야 할지 알수 없다는 것이었다. 마찰에 대한 연구가 없었던 것은 아니었다. 나는 항상 거시적 마찰이나 나노미터 단위의 마찰에 대한 회의인 다중성향의 미국진공학회로부터 환영을 받았다. 그러나 주류의 물리학자들은 그 주제에 아무 관심이 없었다. 거의 대부분의 사람들은 마찰이란 단순히 표면의 울퉁불퉁함에 관계된다고 생각했다. 마찰이 경제에 미치는 영향 또는 일상생활에서 느끼는 마찰의 친숙함을 생각한다면 사람들은 더욱 마찰에 대한 관심을 가졌었을 것이다.

• Journal of radiological science and technology
• /
• v.42 no.1
• /
• pp.39-46
• /
• 2019

This study conducted a comparative analysis of differences between cartesian trajectory in a linear rectangular coordinate system and MultiVane trajectory in a nonlinear rectangular coordinate system axial T1 and axial T2 images using an American College of Radiology(ACR) phantom. The phantom was placed at the center of the head coil and the top-to-bottom and left-to-right levels were adjusted by using a level. The experiment was performed according to the Phantom Test Guidance provided by the ACR, and sagittal localizer images were obtained. As shown in Figure 2, slices # 1 and # 11 were scanned after placing them at the center of a $45^{\circ}$ wedge shape, and a total of 11 slices were obtained. According to the evaluation results, the image intensity uniformity(IIU) was 93.34% for the cartesian trajectory, and 93.19% for the MultiVane trajectory, both of which fall under the normal range in the axial T1 image. The IIU for the cartesian trajectory was 0.15% higher than that for the MultiVane trajectory. In axial T2, the IIU was 96.44% for the cartesian trajectory, and 95.97% for the MultiVane trajectory, which fall under the normal range. The IIU for the cartesian trajectory was by 0.47% higher than that for the MultiVane trajectory. As a result, the cartesian technique was superior to the MultiVane technique in terms of the high-contrast spatial resolution, image intensity uniformity, and low-contrast object detectability.

• Progress in Medical Physics
• /
• v.14 no.1
• /
• pp.28-33
• /
• 2003

The aim of the study was to assess the isocenter deviation between multiple arcs and conformal beams in frameless FSRT. Forty seven patients received single isocenter radiosurgery or therapy (SRS/T) using available framelss FSRT system from Aug. 1997 to Dec. 2m. In choosing multiple arc FSRT or conformal FSRT, we had considered one of two techniques with respect to tumor size and tumor shape. In multiple arc FSRT, the average and standard deviation (SD) of the isocenter deviation was 0.2 mm (SD 0.2 mm), 0.2 mm (SD 0.2) and 0.3 mm (SD 0.2 mm)in the lateral (x), anterior-posterior (y) and cranio-caudal directions (z). In conformal FSRT, the average deviation and SD of the isocenter deviation was 0.2 mm (SD 0.2 mm), 0.3 mm(0.2 mm) and 0.4 mm (SD 0.2 mm) in the x, y and z directions. The average spacial deviation ($\Delta$r) was 0.41 mm and 0.54 mm in multiple arcs and conformal beams, respectively. The isocenter deviation using frameless FSRT system was similar value between multiple arcs and conformal beams. In practice, we believed we can select the appropriate treatment technique according to tumor shape and size.

• New Physics: Sae Mulli
• /
• v.68 no.11
• /
• pp.1183-1191
• /
• 2018

The plasmon behaviors in a superlattice of $GaAs/Al_xGa_{1-x}As$ multiple quantum wells with a half-parabolic confining potential due to different dielectric interfaces are studied under magnetic and electric fields perpendicular and parallel to the superlattice axis by using a previously published theoretical framework. From the density-density correlation functions by considering the intrasubband and the inter-subband transitions under the random phase approximation, we calculate the dispersion energies of the surface and the bulk states as functions of the composition of the multiple quantum well structure and of the magnetic field strength and the average electric field strength over the quantum well. The Raman intensities for various magnetic field strengths and average electric field strengths over the quantum well are also obtained as a function of the energy of the incoming light for these states.

• Progress in Medical Physics
• /
• v.15 no.3
• /
• pp.140-148
• /
• 2004

The absorbed dose for proton beam in water was calculated using the PTRAN code system. The proton interactions with water and the description on absorbed dose calculations are discussed, and the file structure and an execution example of the PTRAN codes are described. For 60, 100, 150, 200, and 250 MeV proton beams it is demonstrated that the absorbed dose is determined from the sum of Coulomb interactions and nuclear reactions, and that the Bragg peak feature depends On the energy straggling and multiple scattering. The PTRAN code was useful for studying the fundamental mechanism of the absorbed dose to water for clinical proton beams.