• 한국정밀공학회지
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• 제24권6호
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• pp.113-120
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• 2007

Chemical vapor deposition (CVD) is one of the various synthesis methods that have been employed for carbon nanotube (CNT) growth. In particular, Ren et al reported that large areas of vertically aligned multi-wall carbon nanotubes could be grown using a direct current (dc) PECVD system. The synthesis of CNT requires a metal catalyst layer, etchant gas, and a carbon source. In this work, the substrates consists of Si wafers with Ni-deposited film. Ammonia $NH_3$) and acetylene ($C_2H_2$) were used as the etchant gases and carbon source, respectively. Pretreated conditions had an influence on vertical growth and density of CNTs. And patterned growth of CNTs could be achieved by lithographical defining the Ni catalyst prior to growth. The length of single CNT was increased as niclel dot size increased, but the growth rate was reduced when nickel dot size was more than 200 nm due to the synthesis of several CNTs on single Ni dot. The morphology of the carbon nanotubes by TEM showed that vertical CNTs were multi-wall and tip-type growth mode structure in which a Ni cap was at the end of the CNT.

• Ocean and Polar Research
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• 제30권1호
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• pp.33-46
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• 2008

In order to investigate seasonal variations of the physical environments in the region of Jinhae Bay-Nakdongpo, we carried out hydrographic surveys from November 2000 to November 2001. Horizontal and vertical distribution of salinity and temperature shows large seasonal variations. Water column is well mixed in winter and stratified in summer. Low-salinity water is distributed in the form of patches because of the drainage control at the Nakdong River. Seasonal variations in the sea near Gadeok-Sudo are affected by topography, river discharge and tidal current. Currents have been measured using a bottom mounted ADCP and DCM12 between November 2000 and August 2001 in the Gadeok-Sudo. The current in the Gadeok-Sudo shows a distinct two-layer structure with reversed current. Low-pass filtered time series of wind, sea elevation and current are coherent for the period of 1-2 days and are attributed to Ekman-like dynamics. Spatial and temporal circulation pattern shows a slight different. The subtidal current in Jinhae Bay goes northward, however is reversed in the Gadeok-Sudo mouth.

• 대한조선학회논문집
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• 제32권1호
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• pp.70-82
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• 1995

본 연구에서는 복잡한 해저지형을 고려한 조류의 거동을 예측하기 위한 3차원 다중기법을 개발하였다. 복잡한 해저지형을 보다 정확하고 효과적으로 고려하기 위하여 연직방향으로 $\sigma$좌표계를 도입하였다. 시간의 전개에 있어서는 계산상의 오차를 감소시키기 위하여 강한 감쇠효과를 가지는 것으로 알려진 Euler backward scheme을 Leapfrog scheme과 결합하여 사용하였다. 또한, 격자체계로는 해의 안정성을 위하여 교차격자체계를 사용하였다. 본 논문에서는, 계산예로서 다양한 해저지형을 가진 직육면체 유체영역을 설정하여 조류의 연직구조와 조류의 방향에 미치는 해저지형의 효과를 조사하였다. 본 연구에서 제안된, 해저지형을 직접적으로 고려한 3차원 다중기법의 계산결과와 2차원 수심평균기법에 의한 계산결과를 비교하여, 조류의 크기와 방향은 특히 복잡한 해저지형을 가지는 천수역에서 해저지형에 의하여 크게 영향을 받음을 알 수 있었다.

• 한국수산과학회지
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• 제24권4호
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• pp.215-228
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• 1991

본 연구는 경험적 직교함수 방법을 적용하여 동해 중서부 해역에서 수직적인 수온 분포의 공간적 특성을 해역별로 구분한 후 특징적인 수온의 수직구조 함수를 제시하였다. 수산진흥원 관측범위 중에서 102-107 정선을 포함하는 동해 중서부 해역은 연안을 따라 남북방향으로 발달하는 북한한류수역, 외해쪽의 동한난류수역과 104정선을 축으로 동서방향으로 발달하는 난수괴역으로 구분되며 동한난류수역은 난수괴역에 의해 남북으로 양분된다. 제2모드함수까지 이용하여 설명되는 수온의 변동성은 북한한류수역에서는 총 분산의$85.20-98.20\%$. 동한난류수역에서는 $85.20-92.90\%$, 난수괴역에서는 $83.50-91.70\%$이다. 가장 많은 분산을 설명하는 수직구조함수의 제1모드는 약 1년의 변동주기를 가지며 해표면에서 극값을 가지는 함수이다 동한난류수역에서는 수온의 변동이 전층에서 동시에 일어나며 북한한류수역과 난수괴역에서는 약 100m 수심과 200m 수심을 경계로 하여 수온의 변동이 반대로 일어난다. 제2모드는 북한한류수역에서는 100m 층에서 극값을 가지며 전 층에서 수온의 변동이 동시에 일어난다. 난수괴역과 동한난류수역에서는 수온의 변화가 반대로 전개되는 교차점을 가진다. 확장된 경험적 직교함수를 적용하여 수직구조함수의 시간에 따른 변화를 고찰한 결과 동해에서 제1모드의 지속성은 4개월 미만이며 북한한류 수역에서의 수직구조함수의 연변화 과정은 동한난류수역과 난수괴역과는 다르게 나타났다.

• 한국수산과학회지
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• 제49권1호
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• pp.61-73
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• 2016

Water mass distribution and currents were investigated off the east coast of Korea near the Hupo Bank using the CTD and ADCP data from June to August 2010. The typical water masses were: (1) Tsushima Surface Water (TSW) from the East Korean Warm Current (EKWC) in the surface layer, (2) a shallow thermocline at 20-30 m depth, (3) Tsushima Middle Water (TMW) of high salinity (>34.2) below the pycnocline, (4) North Korean Cold Water (NKCW) of low salinity (<34.05) and low temperature (<4°C) in the lower layer. In June, a double eddy was observed in which a cold filament intruded cyclonically from the south around a pre-existing cold-core eddy. A burst of strong southward current was recorded in mid-August due to a warm filament from the meandering EKWC. Current in the N-S direction was predominant due to topographic effects, and the direction of the northward EKWC was frequently reversed in its direction due to the eddy-filament activity, whereas the influence of the wind was not noticeable. The vertical structure of the current was of a two-layer system, with the northward EKWC in the upper layer and weak southward flows corresponding to the North Korean Cold Current (NKCC) in the deeper layer.

• 대한전자공학회논문지SD
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• 제44권7호통권361호
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• pp.24-30
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• 2007

본 연구에서는 광 논리 및 광 스위칭 시스템에 응용할 수 있는 수직 구조 레이저 - 완전 공핍 광 싸이리스터 (vertical cavity laser - depleted optical thyristor, VCL-DOT)를 제작하고, 본 연구실에서 제안한 차동 스위칭 방법을 이용하여 광 로직(AND, OR, NAND, NOR, INVERT) 함수를 구현하였고, 그 특성을 측정, 분석하였다. 제작한 VCL-DOT는 0.65 mA의 낮은 레이징 문턱 전류, 0.38 mW/mA의 높은 slope efficiency, 그리고 낮은 입력 광 파워에도 높은 민감도를 보인다. 차동 소자타입의 광 싸이리스터를 이용하면 복잡한 전기 회로를 이용하지 않고도, 집적화된 단일 소자에서 간단한 기준 광입력 시호의 파워를 제어함으로써 다양한 광 로직 게이트를 구현할 수 있다는 장점을 갖는다.

• Earthquakes and Structures
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• 제12권1호
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• pp.135-144
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• 2017

Near-fault ground motions are characterized by high values of the ratio between the peak of vertical and horizontal ground accelerations, which can significantly affect the nonlinear response of a base-isolated structure. To check the effectiveness of different base-isolation systems for retrofitting a r.c. framed structure located in a near-fault area, a numerical investigation is carried out analyzing the nonlinear dynamic response of the fixed-base and isolated structures. For this purpose, a six-storey r.c. framed building is supposed to be retrofitted by insertion of an isolation system at the base for attaining performance levels imposed by current Italian code in a high-risk seismic zone. In particular, elastomeric (e.g., high-damping-laminated-rubber bearings, HDLRBs) and friction (e.g., steel-PTFE sliding bearings, SBs, or friction pendulum bearings, FPBs) isolators are considered, with reference to three cases of base isolation: HDLRBs acting alone (i.e., EBI structures); in-parallel combination of HDLRBs and SBs (i.e., EFBI structures); FPBs acting alone (i.e., FPBI structures). Different values of the stiffness ratio, defined as the ratio between the vertical and horizontal stiffnesses of the HDLRBs, sliding ratio, defined as the global sliding force divided by the maximum sliding force of the SBs, and in-plan distribution of friction coefficient for the FPs are investigated. The EBI, EFBI and FPBI base-isolation systems are designed assuming the same values of the fundamental vibration period and equivalent viscous damping ratio. The nonlinear dynamic analysis is carried out with reference to near-fault earthquakes, selected and scaled on the design hypotheses adopted for the test structures.

• 전자공학회논문지A
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• 제29A권8호
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• pp.78-88
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• 1992

To improve the characteristics of sub$\mu$m short channel MOSFET device, a new device having the convex structure is proposed. This device has 3-dimensionally expandable channel length according to the vertical etched silicon height. For the purpose of comparing the DC and AC characteristics, planar device is also fabricated. Comparing the channel length, the convex device with 0.4$\mu$m silicon height is larger about 0.56$\mu$m in NMOS and 0.78$\mu$m in PMOS than planar devices. DC characteristics, such as threshold voltage, operational current, substrate current and breakdown voltage are compared together with AC characteristics using the ring oscillator inverter delay. Also process and device simulation are performed and the differences between convex and pranaldevice are also compared.

• 한국해양공학회지
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• 제32권4호
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• pp.261-271
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• 2018

In this study, a hydraulic model test, to which Particle Image Velocimetry (PIV) system applied, was used to determine the hydrodynamic characteristics of the advection-diffusion of saltwater according to bottom conditions (impermeable/permeability, diameter, and inclination) and the difference of the initial salt. Considering quantitative and qualitative results from the experiment, the characteristics of the density current were discussed. As an experimental result, the advection-diffusion mechanism of salinity was examined by the shape of saltwater wedge and the flow structure of density currents with various bottom conditions. The vertical salt concentration obtained from the experiment was used as quantitative data to calculate the diffusion coefficient that was used in the numerical model of the advection-diffusion of saltwater.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
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• pp.1011-1015
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• 2005

Fully digital controlled 20-bit magnet power supplies have been developed and successfully tested for closed orbit correction of PLS(Pohang Light Source). The new digital power supply has used fiber optics for 25kHz switching of IGBT drivers, and implemented DSP, ADC, Interlock, DCCT cards in a compact 3U-sized 19" chassis. Input/Output low-pass filters suppress harmonics of 60Hz line frequency and switching frequency noise effectively. Overall performance of the power supplies have been demonstrated as +/- 2ppm short-term stability(<1 min), and +/- 10ppm long-term stability(<36 hours). All the existing 12-bit 70 power supplies for vertical correction magnets will be replaced with new digital power supplies during 2005 summer shutdown period. In this paper, we will describe the hardware structure and control method of the digital power supply and the experimental results will be shown.