• The Korean Journal of Ecology
• /
• 제19권1호
• /
• pp.65-70
• /
• 1996

The daily photosynthetic photon flux density incident on a horizontal surface was estimated with sunshine duration through daily global radiation at Taegu in Korea. The constant and coefficient of $\AA$ngstrom equation for global radiation were calculated as 0.1763 and 0.5012, respectively. The conversion factor from daily global radiation to daily photosynthetic photon flux density was determined as 2.2359.

• Journal of the Optical Society of Korea
• /
• 제15권4호
• /
• pp.321-328
• /
• 2011

Various methods have been investigated to increase photon density in soft tissue, an important factor in low-level laser therapy. Previously we developed a compression-controlled low-level laser probe (CCLLP) utilizing mechanical negative compression, and experimentally verified its efficacy. In this study, we used Bezier curves to numerically simulate the skin deformation and photon density variation generated by the CCLLP. In addition, we numerically modeled changes in optical coefficients due to skin deformation using a linearization technique with appropriate parameterization. The simulated results were consistent with both human in vivo and porcine ex vivo experimental results, confirming the efficacy of the CCLLP.

• 한국광학회:학술대회논문집
• /
• 한국광학회 2000년도 제11회 정기총회 및 00년 동계학술발표회 논문집
• /
• pp.168-169
• /
• 2000

We have tried to enhance the density of the near-field optical memory and to improve the recording/readout speed. The current optical memory has the limitation in both density and speed. This barrier due to the far-field nature can be overcome by the use of the near-field$^{(1)}$ . The optical data storage density can be increased by reducing the size of the nanometric aperture where the near-field is obtained. To fabricate the aperture in precise dimension, we applied the orientation-dependent / anisotropic etching property of crystal Si often employed in the field of MEMS$^{(2)}$ . And so we fabricated the 10$\times$10 aperture array. This array will be also the indispensable part for speeding up. One will see the possibility of the multi-tracking pickup in the phase changing type memory through this array$^{(3)}$ . This aperture array will be expected to write the bit-mark whose size is about 100nm. We will show the recent result obtained. (omitted)

• Journal of the Optical Society of Korea
• /
• 제17권4호
• /
• pp.289-295
• /
• 2013

Although low-level laser therapy (LLLT) has been a valuable therapeutic technology in the clinic, its efficacy may be reduced in deep tissue layers due to strong light scattering which limits the photon density. In order to enhance the photon density in deep tissue layers, this study developed an optical tissue clearing (OTC) laser probe (OTCLP) system which can utilize four different OTC methods: 1) tissue temperature control from 40 to $10^{\circ}C$; 2) laser pulse frequency from 5 to 30 Hz; 3) glycerol injection at a local region; and 4) a combination of the aforementioned three methods. The efficacy of the OTC methods was evaluated and compared by investigating laser beam profiles in ex-vivo porcine skin samples. Results demonstrated that total (peak) intensity at full width at half maximum of laser beam profile when compared to control data was increased: 1) 1.21(1.39)-fold at $10^{\circ}C$; 2) 1.22 (1.49)-fold at a laser pulse frequency of 5 Hz; 3) 1.64 (2.41)-fold with 95% glycerol injection; 4) 1.86 (3.4)-fold with the combination method. In conclusion, the OTCLP system successfully improved the laser photon density in deep tissue layers and may be utilized as a useful tool in LLLT by increasing laser photon density.

• 한국진공학회지
• /
• 제8권2호
• /
• pp.102-110
• /
• 1999

The LIGA X-ray exposure step was modelled into three inequalities, by assuming that the X-ray energy attenuated within a resist is deposited only in the localized range of the resist. From these inequalities, equations for the minimum and maximum exposure times required for a good quality microstructure were obtained. Also, an equation for the thickness of an X-ray mask absorber was obtained from the exposure requirement of threshold dose deposition. The calculation method of the synchrotron radiation power from a synchrotron radiation source was introduced and applied to an X-ray exposure step. A power from a synchrotron radiation source was introduced and applied to an X-ray exposure step/ A power function of photon energy, approximating the attenuation length of the representative LIGA resist, PMMA, and the mean photon energy of the XZ-rays incident upon an X-ray mask absorber were applied to the above mentioned equations. Consequently, the tendencies of the minimum and maximum exposure and with respect to mean photon energy and thick ness of PMMA was obtained. Additionally, the tendencies of the necessary thickness of PMMA and photon energy of the X-ray mask absorber with respect to thickness of PMMA and photon energy of the X-rays incident upon an X-ray mask absorber were examined. The minimum exposure time increases monotonically with increasing mean photon energy for the same total power density and is not a function of the thickness of resist. The minimum exposure time increases with increasing mean photon energy for the same total power density in the case of the general LIGA process, where the thickness of PMMA is thinner than the attenuation length of PMMA. Additionally, the minimum exposure time increases monotonically with increasing thickness of PMMA. The maximally exposable thickness of resist is proportional to the attenuation length of the resist at the mean photon energy with its proportional constant of ln $(Dd_m/D_{dv})$. The necessary thickness of a gold X-ray mask absorber due to absorption edges of gold, increases smoothly with increasing PMMA thickness ratio, and is independent of the total power density itself. The simplicity of the derived equations has made clearly understandable the X-ray exposure phenomenon and the correlation among the exposure times, the attenuation coefficient and the thickness of an X-ray mask absorber, the attenuation coefficient and the thickness of the resist, and the synchrotron radiation power density.

• 대한의용생체공학회:의공학회지
• /
• 제30권1호
• /
• pp.18-22
• /
• 2009

Laser has been widely used in various fields of medicine. Recently, noninvasive low-level laser therapeutic medical devices have been introduced in market. However, low-level laser cannot deliver enough photon density to expect positive therapeutic results in deep tissue layer due to the light scattering property in tissue. In order to overcome the limitation, this study was aimed to develop a negative pressure applied low-level laser probe to optimize laser transmission pattern and therefore, to improve photon density in soft tissue. In order to evaluate the possibility of clinical application of the developed laser probe, ex-vivo experiments were performed with porcine skin samples and laser transmissions were quantitatively measured as a function of tissue compression. The laser probe has an air suction hole to apply negative pressure to skin, a transparent plastic body to observe variations of tissue, and a small metallic optical fiber guide to support the optical fiber when negative pressure was applied. By applying negative pressure to the laser probe, the porcine skin under the metallic optical fiber guide is compressed down and, at the same time, low-level laser is emitted into the skin. Finally, the diffusion images of laser in the sample were acquired by a CCD camera and analyzed. Compared to the peak intensity without the compression, the peak intensity of laser increased about $2{\sim}2.5$ times and FWHM decreased about $1.67{\sim}2.85$ times. In addition, the laser peak intensity was positively and linearly increased as a function of compression. In conclusion, we verified that the developed low-level laser probe can control the photon density in tissue by applying compression, and therefore, its potential for clinical applications.

• 한국컴퓨터그래픽스학회논문지
• /
• 제30권3호
• /
• pp.141-147
• /
• 2024

점진적 광자 매핑 방식은 복잡한 전역 조명 효과를 효율적으로 렌더링할 수 있다. 그러나 샘플이 유한한 경우, 반경 축소비율 변수에 의해 분산과 편향 값이 크게 영향 받는다. 유한한 샘플을 사용한 렌더링 결과의 픽셀 오류 및 기울기를 추정하여 추정된 기울기를 기반으로 반경 축소비율을 결정하는 최적의 매개변수를 학습할 수 있다면, 렌더링 된 이미지의 오류를 줄일 수 있을 것이다. 본 논문에서는 점진적 광자 매핑 방식을 통한 렌더링과 매개변수 학습이 동시에 될 수 있도록 기울기를 추정하고 추정된 기울기를 유한 차분법을 통해 계산된 기울기와 비교하여 검증한다. 본 논문에서 추정된 기울기는 향후 점진적 광자 매핑 방식의 렌더링과 매개변수 추정을 동시에 수행하는 온라인 학습 알고리즘에 적용될 수 있을 것으로 기대된다.

• 한국정밀공학회지
• /
• 제26권6호
• /
• pp.36-40
• /
• 2009

Development of maskless lithography techniques can provide a potential solution for the photomask cost issue. Furthermore, it could open a market for small scale manufacturing applications. Since femtosecond lasers have been found suitable for processing of a wide range of materials with sub-micrometer resolution, it is attractive to use this technique for maskless lithography. As a femtosecond laser has recently been developed, both of high power and high photon density are easily obtained. The high photon density results in photopolymerization of photoresist whose absorption spectrum is shorter than that of the femtosecond laser. The maskless lithography using the two-photon absorption (TPA) makes micro structures. In this paper, we present a femtosecond laser direct write lithography for submicron PR patterning, which show great potential for future application.

• Transactions on Electrical and Electronic Materials
• /
• 제13권1호
• /
• pp.16-18
• /
• 2012

LED lighting systems that combine lighting capability, emotional and physiological characteristics are required for lighting source and multifunctional applications. In this work, Simulation studies using optical analysis software packages, Light Tools, are presented. This is done to estimate the uniformity ratio of illuminance and photosynthetic photon flux density (PPFD) of the periodic 2D lattice arrangements, such as square, diamond, two-way bias quadrangular, hexagonal, and Kagome lattices, under the same transmissivity, absorptance and reflectivity. It has been found out that the two-dimensional Kagome lattice arrangement exhibited high uniformity ratio of illuminance and PPFD compared to other lattices. Accordingly, these results can be used to guide a design and improve the lighting environment which in turn would maximize the uniform distributions of illuminance.

• Journal of Astronomy and Space Sciences
• /
• 제38권1호
• /
• pp.55-63
• /
• 2021

The universe is well known to be consists of dark energy, dark matter and the standard model (SM) particles. The dark matter dominates the density of matter in the universe. The dark matter is thought to be linked with dark photon which are hypothetical hidden sector particles similar to photons in electromagnetism but potentially proposed as force carriers. Due to the extremely small cross-section of dark matter, a large amount of data is needed to be processed. Therefore, we need to optimize the central processing unit (CPU) time. In this work, using MadGraph5 as a simulation tool kit, we examined the CPU time, and cross-section of dark matter at the electron-positron collider considering three parameters including the center of mass energy, dark photon mass, and coupling constant. The signal process pertained to a dark photon, which couples only to heavy leptons. We only dealt with the case of dark photon decaying into two muons. We used the simplified model which covers dark matter particles and dark photon particles as well as the SM particles. To compare the CPU time of simulation, one or more cores of the KISTI-5 supercomputer of Nurion Knights Landing and Skylake and a local Linux machine were used. Our results can help optimize high-energy physics software through high-performance computing and enable the users to incorporate parallel processing.