• 한국레이저가공학회지
• /
• 제16권2호
• /
• pp.1-6
• /
• 2013

Picosecond lasers are a very effective tool for micromachining metals, especially when high accuracy, high surface roughness and no heat affected zone are required. However, low productivity has been a limit to broadening the spectrum of their industrial applications. Recently it was reported that in the micromachining of copper with a 1064nm picosecond laser, there exist the optimal pulse energy and repetition rate to achieve the maximum volume ablation rate. In this paper, we used a 515nm picosecond laser, which is more efficient for micromachining copper in terms of laser energy absorption, to obtain its optimal pulse energy and repetition rate. Theoretical analysis based on the experimental data on copper ablation showed that using a 515nm picosecond laser instead of a 1064nm picosecond laser is more favorable in that the calculated threshold fluence is 75% lower and optical penetration depth is 50% deeper.

• 한국통신학회논문지
• /
• 제37권8A호
• /
• pp.689-697
• /
• 2012

본 논문은 무선 채널 환경에서 H.264 스케일러블 비디오 코딩으로 부호화된 비디오 데이터의 전송 성능 개선과 신뢰성 향상을 위해 기본계층 반복 전송과 HARQ를 제안하고 그 성능을 확인하고 있다. 제안 방법은 향상계층을 제외하고 기본계층에만 적용되기 때문에, 무선자원의 부족과 전송 지연의 문제들도 해결해 줄 수 있다. 수치 결과 제안 방법은 SNR=3.4dB 기준으로 $1.5{\times}10^{-5}$의 BER 성능을 보였고, 동일 SNR에서 $1.2{\times}10^{-3}$의 성능을 보여 주었다. 또한 실험 영상 결과를 통해서도 제안 방법이 무선 링크에서 SVC 성능을 개선함을 확인하였다.

• 말소리와 음성과학
• /
• 제12권1호
• /
• pp.1-9
• /
• 2020

The perceptual assimilation of a nonnative phonological contrast can change with linguistic experience, resulting in naïve listeners and novice second language (L2) learners potentially assimilating the members of a nonnative contrast to different native (L1) categories. While it has been shown that this sort of change can affect the discrimination of the nonnative contrast, it has not been tested whether such a change could have consequences for the production of the contrast. In this study, L1 speakers of Mandarin Chinese who were (1) naïve to Korean, (2) novice L2 learners, or (3) advanced L2 learners participated in a Korean non-word repetition task using word-initial sibilants. The initial CVs of their repetitions were then played to L1 Korean listeners who categorized the initial consonant. The naïve talkers were more likely to repeat an initial /s^ha/ as an affricate, whereas the L2 learners repeated it as a fricative, in line with how these listeners have been shown to assimilate Korean sibilants to Mandarin categories. This result suggests that errors in the production of new words presented auditorily to nonnative listeners may be driven by how they perceptually assimilate the nonnative sounds, emphasizing the need to better understand what drives changes in perceptual assimilation that accompany increased linguistic experience.

• 한국통신학회논문지
• /
• 제33권6C호
• /
• pp.520-528
• /
• 2008

현재 웹 콘텐츠의 다양화로 인해 콘텐츠의 관리를 위한 CMS(Contents Management System)가 다양하게 운영되고 있다. 그러나 각 업체의 CMS는 서로 다양한 형태의 메타데이터로 관리되고 있어, 웹 콘텐츠의 중복이 심각한 실정이다. 또한 일부 CMS에서 부분 지원하는 콘텐츠 보호만으로 풍부한 웹 콘텐츠의 저작권 기술을 보호하기는 매우 어렵다. 따라서 본 논문에서는 메타데이터를 기반으로 상호 이질적인 CMS의 연동을 통한 웹 콘텐츠의 중복을 해결 하였다. 또한 각 CMS를 기반으로 공유된 콘텐츠는 콘텐츠의 보호를 위해 웹 콘텐츠 인증코드를 이용한 DRM(Digital Rights Management) 기술을 기반으로 콘텐츠 사용 제한 및 저작권 보호를 지원함으로 다량의 콘텐츠 사용에 매우 안전함으로 유용하게 사용될 수 있다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1999년도 하계학술대회 논문집 E
• /
• pp.2192-2194
• /
• 1999

In this study, We have accomplished a new approach to develope a cheap and compact pulsed $CO_2$ laser system. We used a fast SCR as switching device instead of a thyatron in the pulsed power supply. Using the Pulse transformer, energy in the condenser is tranferred to the secondary, electrodes of discharge tube, from the primary. An axial and water cooled type was adopted as the laser cavity. The laser performance characteristics as various parameters, such as gas pressure and pulse repetition rate, have been investigated. As a result, the maxium laser output was 12.3[W] at a pulse repetition rate of 120[pps] and a filling pressure of 12[Torr].

• 복식문화연구
• /
• 제17권6호
• /
• pp.972-980
• /
• 2009

This study was aimed to develop ume flower image into a competitive fashion culture product image by reinterpreting the image in modern terms, manufacturing patterns and applying them to various items. In terms of method, ume flower petal was used as a motive and developed into a pattern, using Adobe Illustrator 10, a computer design program. Based on the symbolic image and realist form of ume flower, three new basic motives of new figurative image were set using form omission, simplification, overlapping, repetition and graphic elements. Each motive developed transformed patterns through the change, transformation, combination of colors. The repetitive unit of each motive set expressed geometrical patterns and combination of flower patterns using pattern repetition and $45^{\circ}$ repetition technique in combination with the check arrangement using quadrangle, and set the direction of design that would fit for each item of fashion culture products. Also, consistency and practicality were sought in the goods planning composition of each item by applying motive pattern results to the fashion culture goods, such as neckties, scarves, T-shirts that can be consumed in everyday life. It seems that more creative culture goods including ume flowers will be developed by seeing our own cultural elements as well as flower patterns like ume flower with modern trends.

• 전기학회논문지
• /
• 제64권8호
• /
• pp.1207-1211
• /
• 2015

Various laser systems have been widely used in almost all industrial technologies because they have high energy density, directivity and coherence. Recently the clinical application is becoming wider in medical parts such as incurable disease, diagnosis and so on. Generally, ruby laser beam has the greatest efficacy for removing tattoos, freckle and other skin problem. But current medical ruby laser system has the maximum repetition rate of 2Hz and optical output beam energy of 1J. Many medical doctors really want to have a high repetition ruby laser system because that can reduce the operation time. We investigated a new ruby laser system with high repetition rate of 4Hz using double cavities. Furthermore, we develop a new power supply system adopting zero voltage switching(ZVS) to minimize switching loss by LLC resonant converter designed as 2kW class.

• 국제물리치료학회지
• /
• 제11권3호
• /
• pp.2147-2154
• /
• 2020

Background: Improperly conducted exercise may lead to worsening of musculoskeletal complications. Such may worsen due to increased repetition and intensity during exercise. In addition, different responses may show different needs for training program. Objectives: To compare kinematics of symmetric concentric and eccentric motions during increased repetitions and intensities for men and women. Design: Quasi-randomized trial. Methods: A total of ten men and eleven women participated in this study. Concentric and eccentric motions of the lateral raises were observed for initial positions of abduction and adduction. Low and high exercise intensities were applied, and 15 repetitions were conducted for both intensities. Initial, 3 inbetween repetitions, and last repetition were recorded for comparisons. Results: The concentric or abduction motions showed no significant differences for all comparisons. However, eccentric or adduction motions showed greater significant differences as the exercise intensity increased for both men and women. Such significant differences were most prevalent during the first and last repetitions with greatest differences during the initial repetitions. Conclusion: Kinematic difference between men and women during increased repetitions and intensity indicate the need for more individualized exercise intervention and consideration between men and women. Individualized interventions may prevent exercise-induced postural abnormality and corresponding musculoskeletal dysfunction.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제49권9호
• /
• pp.541-545
• /
• 2000

We propose a pulsed $CO_2$laser below 30W by the AC(60Hz) switching control of leakage transformer primary which has some advantages of cost and size compared to a typical pulsed power supply. Pulse repetition rate is adjusted from 5 Hz to 60 to Hz control laser output. In this laser a low voltage open loop control for high voltage pulse discharge circuit is employed to aviod the Hv sampling or switching and high voltage leakage transformer is used to convert low voltage pulse rectified from AC to high voltage one. A ZCS(Zero Crossing Switch) circuit and a PIC(programble one-chip microprocessor are used to control gate signal of SCR precisely. The pulse repetition rate is limited by 60Hz due to the frequency of AC line and a high leadkage inductance. The maximum laser output was about 23 W at pulse repetition rate of 60Hz total gas mixture of $CO_2$ : $N_2$ : He=1: 9: 15 and total pressure of 18 Torr

• 한국의류학회지
• /
• 제33권5호
• /
• pp.817-826
• /
• 2009

As UV radiation to the earth increased over recent years, many adverse effects of UV radiation have been reported. There are needs to develop UV-protective apparel and accessaries to protect skin from these harmful effects. Cellulose is one of the most frequently worn fiber during summer time. However, celllulose shows very low UV-protective property especially in case of thin and low fabric content. In this study, UV-protective cellulose textiles were developed using chiotsan mordanting and green tea dyeing. The repetition effect of chitosan and green tea treatment were focused. Three different cellulose fibers, cotton, linen, and ramie, were used for this study. All chitosan mordanted and green tea dyed fabrics showed increases in UV-protective property. The color of fabrics tended to darker as the numbers of mordanting process and green tea dyeing increased. UV-protective property did not increase significantly upon the repetition of mordanting and green tea dyeing treatment except ramie fabric. UV protective property was persisted upon washfastness test in all three cellulose fiber types.