• Journal of the Optical Society of Korea
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• 제19권6호
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• pp.638-642
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• 2015

We present a simple method to determine the focal distances of lenses with the Talbot self-images. This method uses only one grating, and a priori knowledge of the period of the grating is replaced with a linear relation between the (de)magnified periods of the Talbot images and the lens-to-grating distance. A thick lens whose effective focal length is 500 mm was used to validate the method, and the focal distance of the converging beam was determined with the difference of 0.15% for the nominal focal distance of 521.9 mm. The determined period of the grating with the difference of 0.2% also supports the validation.

• 지질공학
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• 제1권1호
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• pp.121-136
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• 1991

본 연구에서는 P파형의 초동극성 분포를 이용하여 홍성지진의 Focal Mechanism을 평가하였다. 비선형 전산처리과정을 이용하여 원지진진앙거리에서 관측된 9개의 P파형의 초동극성 분포와 주향, 경사 및 상반변위방향의 변화로부터 구한 Focal Mechanism과의 부합성을 조사하였다. 위의 과정을 이용하여 처리한 결과 주단층면의 주향 및 겅사는 약 247도 및 약 78도로서 홍성부근지역의 선구조와 잘 일치함을 보여주었다. 그러나, 주단층면의 상반변위 방향은 약 40도에서 약 160도 까지의 광범위한 값을 보여주었으나, 이는 관측점의 방위각 분포가 불충분하기 때문인 것으로 분석되었다. 위에서 결정된 Focal Mechanism이 의미하는 주응력 방향은 일본 트렌치를 따라서 태평양판이 유라시아판 아래로 Subduction할 때 가능한 지응력장가 상반되지 않음을 보여 주었다. 또한, 이러한 Focal Mechanism으로부터 원자력발전소나 핵폐기물 처리장 및 처분장 건설시, 부지고유응답 스펙트럼 및 강지진동 자료와 같은 내진설계기준을 위해 필요한 한반도의 지진지체구조 특성에 대한 정보를 얻을 수 있다.

• 대한기계학회논문집B
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• 제32권10호
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• pp.784-790
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• 2008

The feasibility and the accuracy of the correlation coefficient(CC) method for the determination of particle positions along the optical axis in digital particle holography were verified by alidation experiments. A traverse system with capable of high precision was used to move the particle objects by exact known distances between several different positions. The particle positions along the optical axis were calculated by the CC method and compared with their exact values to obtain the errors of the focal plane determination. The tested particles were 2D dots in a calibration target along with different sized glass beads and droplets that reflected and caused a three-dimensional effect. The results show that the CC method can work well for both the 2D dots and the 3D particles. The effect of other particles on the focal plane determination was also investigated. The CC method can locate the focal plane of particles with a high precision, regardless of the existence of other particles.

• ETRI Journal
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• 제45권2호
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• pp.291-303
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• 2023

Selfies are a popular form of photography. However, due to physical constraints, the compositions of selfies are limited. We present algorithms for creating virtual portraits with interesting compositions from a set of selfies. The selfies are taken at the same location while the user spins around. The scene is analyzed using multiple selfies to determine the locations of the camera, subject, and background. Then, a view from a virtual camera is synthesized. We present two use cases. After rearranging the distances between the camera, subject, and background, we render a virtual view from a camera with a longer focal length. Following that, changes in perspective and lens characteristics caused by new compositions and focal lengths are simulated. Second, a virtual panoramic view with a larger field of view is rendered, with the user's image placed in a preferred location. In our experiments, virtual portraits with a wide range of focal lengths were obtained using a device equipped with a lens that has only one focal length. The rendered portraits included compositions that would be photographed with actual lenses. Our proposed algorithms can provide new use cases in which selfie compositions are not limited by a camera's focal length or distance from the camera.

• 한국광학회지
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• 제8권1호
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• pp.19-25
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• 1997

Agfa 8E75HD 사진건판에서 얻은 dichromated gelatin(DCG) 박막에 구면파와 평면파를 간섭시켜 holographic zone plate(HZP)를 만들었다. DCG박막의 비서형적인 광학특성들을 고려하여 HZP의 이론식을 유도하였다. 이 이론식에 의한 HZP의 초점거리를 거리는 f. f/2, f/3, f/4, ... 였으며, 실험적으로도 평면파를 입사하여 6개까지의 해당 초점들을 관측하였다. 칼날 주사 방법으로 측정한 첫 번째 재생 초점 근처에서의 빔의 모양은 Gaussian 분포를 가짐을 확인하였다.

• 한국정밀공학회지
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• 제27권3호
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• pp.18-26
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• 2010

Diffraction gratings with precise spatial periods of 2 ${\mu}m$ and 5 ${\mu}m$ have been fabricated by using a femtosecond laser which does not have limits on materials of micromachining and small thermal effects due to high peak power. Diffraction angle and diffraction efficiency of those were measured. Simulation results of diffraction angle and diffraction efficiency of the diffraction grating calculated with the parameters such as line width, depth, and spatial period of the fabricated gratings were compared with experimental results measured with a He-Ne laser. Besides these, Fresnel Zone Plates (FZPs) with focal distances of 50 mm and 25 mm were fabricated and focal distances of fabricated FZP were measured. Those experimental results for diffraction gratings and FZPs match well with experimental results.

• 대한방사선기술학회지:방사선기술과학
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• 제21권1호
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• pp.52-58
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• 1998

We can and must improve the diagnostic images using available knowledge and technology. At the same time we must strive to reduce the patient's integral and entrance radiation dose. Reducing the integral dose to the patient during the radiologic procedure is a primary concern of the patient, especially the pediatric patient, the radiologist and the technologist. A 100cm focal film distance generally is used for most over-table radiography. The early x-ray tubes and screen film combinations required long exposures, which often resulted in motion artifacts. But nowaday, we have the generators and x-ray tubes that can deliver the energy necessary in a very short time and the receptors that can record the information just as rapidly. And, we performed this studies to evaluate the patient exposure dose and the image quality by increasing focal film distance in diagnostic radiography. There are many factors which affected to exposure factor, but we studied to verify of FFD increase, only. Effect of increasing the focal film distance to a 140 cm distance was tested as follows; 1. The focal film distances were set at 100, 120, and 140cm. 2. A 18cm acryl(tissue equivalent) phantom was placed on the table top. 3. An Capintec 192 electrometer with PM 05 ion chamber was placed at the entrance surface of the phantom, and exposure were made at each focal film distances. 4. The procedure was repeated in the same manner as above except the ion chamber was placed beneath the phantom at the film plane. 5. Exit exposure were normalize to 8mR for each portions of the experiment. Based on the success of the empirical measurements, a detailed mathematical analysis of the dose reduction was performed using the percent depth dose data. The results of this study can be summerized as followings ; 1) Increasing FFD from 100 cm to 140 cm, we would create a situation that would have a significant effect on the overall quality of radiograph and achive the 17.42% reduction of entrance dose and the 18.95% reduction of integral dose that the patient receives. 2) Thickness of Al step wedge for equal film density increased with the long distance. 3) Increasing FFD, Magnification of image was lowered. 4) Resolution of image also increased with the FFD. As the results described above, we strongly recommend using the long FFD to provide better information for our patients and profession in abdomen radiographic studies.

• 한국지진공학회논문집
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• 제11권6호
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• pp.33-39
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• 2007

2004년 5월 29일 발생한 울진지진에 대해 지진원 상수(지진원기구, 진원깊이, 규모, 지진원 특성 등)를 모멘트텐서 방법을 이용하여 분석하였다. 3종류의 지각모델에 대해 지각응답함수를 구하여 분석에 이용하였다. 또한 최적의 지진원 상수값을 분석하기 위해 3종류의 진앙위치를 고려하여 분석하였다. 관측소의 방위각 분포 및 진앙거리에 대해서 결과값에 약간의 영향을 주었다. 6개의 모멘트텐서 성분을 조합하여 분석한 결과 울진지진은 거의 남북방향의 주향을 가진 전형적인 역단층의 운동에 의해 발생되었다. 분석된 지진원 기구는 울진지진 진앙 주변은 동서방향의 압축방향을 가진 지체역학적인 환경을 가지고 있는 것으로 제시하고 있다. 진원깊이는 약 12km의 값을 가지고 있다. 지진원기구는 기존의 연구결과와 유사하나 진원깊이는 다소 차이가 존재하였다. 이러한 차이는 방법론, 자료 종류 또는 지진원 고유의 기하학적 형태 등에 기인하는 것으로 해석된다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2007년도 공동학술대회 논문집
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• pp.69-74
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• 2007

The source mechanism parameters of the Ulgin earthquake on 29 May 2004 are analyser using moment tensor inversion technique. The Green's function are calculated for the Kim's(1985) crust model of southern Korean Peninsula. Results derived from the Ulgin earthquake show the dependence of azimuthal station distribution and epicentral distances. final results show fairly good agreement to those of other authors. the focal mechanism for the Ulgin earthquake is found to be oblique reverse motion with NNE strike. The focal depth is estimated to be 10-12km.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.433-433
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• 2016

Carbon nanotubes (CNT) emitter has widely become an attractive mechanism that draws growing interests for cold cathode field emission. CNT yarns have demonstrated its potential as excellent field emitters. It was demonstrated that a small focal spot size was achieved by manipulating some electrical parameters, such as applied bias voltage at the mesh gate, and electrostatic focal lenses, geometrical parameters, such as axial distances of the anode, and the electrostatic focal lens from the cathode assembly, and the dimension of the opening of the electrostatic lens. Electrical-optics software was used to systematically investigate the behavior of the electron beam trajectory when the aforementioned variables were manipulated. The results of the experiment agree with the theoretical simulation results. Each variable has an individual effect on the electron beam focal spot size impinging on the target anode. An optimum condition of the parameters was obtained producing good quality of X-ray images. Also, MWCNT yarn was investigated for field emission characteristics and its contribution in the X-ray generation. The dry spinning method was used to fabricate MWCNT yarn from super MWCNTs, which was fabricated by MW-PECVD. The MWCNT yarn has a significant field emission capability in both diode and the triode X-ray generation structure compared to a MWCNT. The low-voltage-field emission of the MWCNT yarn can be attributed to the field enhancing effect of the yarn due to its shape and the contribution of the high-aspect-ratio nanotubes that protrude from the sides of the yarn. Observations of the use of filters on the development of X-ray images were also demonstrated. The amount of exposure time of the samples to the X-ray was also manipulated. The MWCNT yarn can be a good candidate for use in the low voltage field emission application of X-ray imaging.