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      • WCDMA용 67-dB DR, 1.2-V, $0.18-{\mu}m$ 시그마-델타 모듈레이터 설계

        김현중,유창식,Kim, Hyun-Jong,Yoo, Chang-Sik 대한전자공학회 2007 電子工學會論文誌-SD (Semiconductor and devices) Vol.44 No.6

        [ $0.18-{\mu}m$ ] CMOS 공정에서 1.2-V 2차 Full-Feedforward 구조의 ${\Sigma}{\Delta}$ 모듈레이터를 설계하였다. Full-Feedforward 구조는 Op-Amp의 성능 요구치를 크게 경감시키기 때문에 저전압 저전력 ${\Sigma}{\Delta}$ 모듈레이터를 만들기에 적합한 구조로 세계적으로 많이 채택되고 있는 추세이다. 그리고, Top-Down 설계 기법을 적용하여 ${\Sigma}{\Delta}$ 모듈레이터를 설계하였는데, 이를 위하여 Op-Amp의 유한한 DC-Gain과 Bandwidth 등 여러 가지 비이상적 효과들을 모델링하여 전달함수를 유도하였다. [ $0.18-{\mu}m$ ] CMOS 1.2-V 2nd-order ${\Sigma}{\Delta}$ modulator with full-feedforward topology is designed. Using full-feedforward topology makes op-amp performance requirements much less stringent, therefore it has been adopted as a good candidate for low-voltage low-power applications throughout the world. Also, ${\Sigma}{\Delta}$ modulator is designed with top-down design approach, therefore various nonideal effects of op-amp are modeled in this paper.

      • KCI등재

        Computation of the Nielsen type numbers for maps on the Klein bottle

        김현중,이종범,유원석 대한수학회 2008 대한수학회지 Vol.45 No.5

        Let f : M → M be a self-map on the Klein bottle M. We compute the Lefschetz number and the Nielsen number of f by using the infra-nilmanifold structure of the Klein bottle and the averaging formulas for the Lefschetz numbers and the Nielsen numbers of maps on infranilmanifolds. For each positive integer n, we provide an explicit algorithm for a complete computation of the Nielsen type numbers NPn(f) and NΦn(f) of fn. Let f : M → M be a self-map on the Klein bottle M. We compute the Lefschetz number and the Nielsen number of f by using the infra-nilmanifold structure of the Klein bottle and the averaging formulas for the Lefschetz numbers and the Nielsen numbers of maps on infranilmanifolds. For each positive integer n, we provide an explicit algorithm for a complete computation of the Nielsen type numbers NPn(f) and NΦn(f) of fn.

      • KCI등재

        퍼킨서스편모충 (Perkinsus olseni) 의 휴면포자와 유주자 형성에 수온과 염분이 미치는 영향

        김현중,방인석,박경일 한국패류학회 2010 The Korean Journal of Malacology Vol.26 No.3

        The genus Perkinsus are parasitic protozoans that cause massive inflammatory responses in infected marine shellfish worldwide. This ultimately leads to great economic losses. This study examined the effects of water temperature and salinity on the formation of prezoosporangia and zoosporangia in order to understand the ecology of the pathogens. The induction of prezoosporangia from trophozoites occurred readily at higher water temperatures (20 and 30°C) and they had larger diameters than those incubated at lower temperatures (4 and 10°C). The formation of zoospores in prezoosporangia was also strongly influenced by water temperature and salinity; prezoosporangia exposed to water temperatures of 20 and 30°C and salinities of 20 and 30 ppt had high rates of zoosporulation, while no or very low rates of zoosporulation were observed at temperatures below 10°C or salinity below 10 ppt. Our data will be useful for the development of strategies to counter P. olseni proliferation in Korean waters. 퍼킨서스편모충 P. olseni는 우리나라 바지락의 대부분이감염되어 있으며 극심한 염증을 유발하는 우리나라 바지락의대표적 기생충이다. 본 연구에서는 퍼킨서스편모충의 생태학적 특성을 조사하고자 영양체에서 휴면포자로 전환되는 과정과 유주자를 형성하는 과정에서 수온과 염분이 미치는 영향을조사하였다. 조사결과 영양체에서 휴면포자로의 유도는 수온이 높을수록 유도율이 높고 휴면포자의 직경이 커지는 현상이관찰되었다. 또한 유주자 형성은 고수온, 고염분의 환경에서잘 형성됨으로써 10℃이하에서는 유주자 발생이 이루어지 않으며, 10 ppt에서는 유주자 형성이 급격히 감소하고 5 ppt에서는 유주자 발생이 이루어지지 않음이 확인되었다. 이러한 퍼킨서스편모충의 생태학적 정보는 이 질병의 구제 대책 수립에중요한 정보를 제공할 수 있을 것으로 기대된다.

      • KCI등재

        토목섬유로 보강한 흙 시료의 일축 및 삼축 압축거동 해석

        김현중,김윤진,변성원,주창환,전한용,Kim, Hyun-Joong,Kim, Yoon-Jin,Byun, Sung-Won,Jo, Chang-Whan,Jeon, Han-Yong 한국섬유공학회 2009 한국섬유공학회지 Vol.46 No.3

        In this study, the effects of geosynthetics reinforcements on compressive behaviors of weathered granite soils were investigated by uni-axial and tri-axial compression tests. Geogrid, geomat, and polyethylene slit film fiber were used as reinforced geosynthetis. From the experimental results, these geosynthetics reinforcement effects could increase the compressive strength of soil and especially, the reinforced effects of geogrid and geomat were extremely excellent compared to polyethylene slit film fiber reinforced. This effect is larger for 3 layer geosynthetics used. For triaxial compression test, despite unconsolidated undrained condition, it is seen that the increasing shear strength of the weathered granite soils is due to the increasing adhesive power.

      • KCI등재

        관상동맥 질환의 중재시술 후에 측정한 Thrombolysis in Myocardial Infarction Frame Count에 따른 좌심실 수축기능의 변화

        김현중,한성우,김성해,서순용,정상만,유규형 대한심장학회 2008 Korean Circulation Journal Vol.38 No.12

        Background and Objectives: Some reports have suggested that coronary microvascular dysfunction plays a role in the recovery of myocardial function in patients with obstructive coronary artery disease. Thrombolysis in myocardial infarction (TIMI) frame count (TFC) is regarded as a simple, reliable method for evaluating microvascular function. We evaluated microvascular function using TFC immediately after coronary intervention and compared TFC with left ventricular systolic function eight months later. Subjects and Methods: We studied 68 patients with obstructive coronary artery disease who underwent coronary intervention. Just after intervention, TFC was calculated with the standard method. Left ventricular systolic function was assessed with left ventricular diastolic dimension (LVEDd), ejection fraction (EF), and wall motion score index (WMSI). Eight months after intervention, we completed follow-up coronary angiography and echocardiography. We defined high TFC (HTFC) as a TFC greater than 18. Results: Ten patients were in the HTFC group, and 58 patients were in the low TFC (LTFC) group. There was no difference between the two groups with regard to baseline cardiovascular characteristics and angiographic findings. Just after intervention, the HTFC group showed significantly higher LVEDd (56.6±8.9 mm) and WMSI (1.60±0.65) compared to the LTFC group (50.3±5.9 mm, p<0.05; 1.34±0.29, p<0.05, respectively), but there was no significant difference in EF between the groups (49.3±18.6% vs. 56.2±14.8%, p> 0.05). Eight months after intervention, there was also a significant decrease in the WMSI in the LTFC group (1.23±0.25, p<0.05), but not in the HTFC group (1.57±0.62, p>0.05). Conclusion: Increased TFC immediately after coronary intervention is an important poor prognostic factor related to myocardial systolic function eight months after coronary intervention. Coronary microvascular dysfunction may influence myocardial recovery in the setting of obstructive coronary artery disease. Background and Objectives: Some reports have suggested that coronary microvascular dysfunction plays a role in the recovery of myocardial function in patients with obstructive coronary artery disease. Thrombolysis in myocardial infarction (TIMI) frame count (TFC) is regarded as a simple, reliable method for evaluating microvascular function. We evaluated microvascular function using TFC immediately after coronary intervention and compared TFC with left ventricular systolic function eight months later. Subjects and Methods: We studied 68 patients with obstructive coronary artery disease who underwent coronary intervention. Just after intervention, TFC was calculated with the standard method. Left ventricular systolic function was assessed with left ventricular diastolic dimension (LVEDd), ejection fraction (EF), and wall motion score index (WMSI). Eight months after intervention, we completed follow-up coronary angiography and echocardiography. We defined high TFC (HTFC) as a TFC greater than 18. Results: Ten patients were in the HTFC group, and 58 patients were in the low TFC (LTFC) group. There was no difference between the two groups with regard to baseline cardiovascular characteristics and angiographic findings. Just after intervention, the HTFC group showed significantly higher LVEDd (56.6±8.9 mm) and WMSI (1.60±0.65) compared to the LTFC group (50.3±5.9 mm, p<0.05; 1.34±0.29, p<0.05, respectively), but there was no significant difference in EF between the groups (49.3±18.6% vs. 56.2±14.8%, p> 0.05). Eight months after intervention, there was also a significant decrease in the WMSI in the LTFC group (1.23±0.25, p<0.05), but not in the HTFC group (1.57±0.62, p>0.05). Conclusion: Increased TFC immediately after coronary intervention is an important poor prognostic factor related to myocardial systolic function eight months after coronary intervention. Coronary microvascular dysfunction may influence myocardial recovery in the setting of obstructive coronary artery disease.

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