• ALGAE
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• v.23 no.3
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• pp.241-250
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• 2008

Since seagrasses in the coastal and estuarine ecosystems achieve high levels of production, they require high inorganic carbon and nutrient incorporation. Thus, seagrasses may play a significant role in carbon and nutrient cycling in the coastal and estuarine ecosystems. To examine growth dynamics of Zostera marina L. environmental factors such as underwater irradiance, water temperature, and salinity, and biological parameters such as shoot density, biomass, shoot morphology, and leaf productivity were measured in two bay systems (Jindong Bay and Gamak Bay) on the southern coast of Korea. While underwater irradiance did not show distinct seasonal trend, water temperature at both sites exhibited clear seasonal trend throughout the experimental period. Shoot density increased dramatically during winter due to the increased seedlings through germination of seeds in Jindong Bay and due to the increased lateral shoots in Gamak Bay. Eelgrass biomass increased during winter and decreased during summer. Maximum biomass in Jindong Bay and Gamak Bay was 250.2 and 232.3 g dry weight m–a2, respectively. Carbon incorporation into the eelgrass leaf tissues was estimated from productivity and leaf tissues carbon content. The calculated annual carbon incorporations at the Jindong Bay and Gamak Bay sites were 163 and 295 g C m–`2 y–`1, respectively. This high carbon incorporation into seagrass tissues suggests that seagrass habitats play an important role as a carbon absorber in the coastal and estuarine ecosystems.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.2
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• pp.112-118
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• 2004

Recently, development of rare earth permanent magnet with the high remanence, high coercivity allows the design of brushless motors with very high efficiency over a wide speed range. Cogging torque is produced in a permanent magnet by magnetic attraction between the rotor mounted permanent magnet and the stator teeth. It is an undesired effect that contributes to output ripple, vibration, and noise of machine. This cogging torque can be reduced by variation of magnet arc length, airgap length, magnet thickness, shifting the magnetic pole and varying the radial shoe depth and etc. In this paper, some airgap length and magnet arc that reduce cogging torque are found by finite element method(FEM) and Maxwell stress tensor method. The SPM(Surface Permanent Magnet) type of high-power Brushless DC (BLDC) motor is optimized as a sample model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.3
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• pp.13-24
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• 1993

The influence of the bubble structure and strength characteristics on the freeze-thaw resistance of high strength concrete is investigated by the laboratory experiment. The test conditions are formed in the manner that water is continueusly supplied externally and the specimens were received severe weather actions from ordinary to significantly low temperatures. The experiments are performed in two stages. In the first stage, the relation between the durability to frost action and the bubble structure is analyzed especially with respect to the water-cement ratio and the amount of air. The AE and non-AE concrete specimens made of ordinary portland cement are used in the test. In the second stage, the non-AE concrete specimens using vibratory compaction to improve the durability to frost action, and the high watertight specimens of rapid hardening portland cement to increase their initial strength are produced and tested. The degree of watertightness of the specimens is determined by measuring the permeability of the specimens and the bubble structure of the high watertight concrete is also estimated.

• Composites Research
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• v.12 no.1
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• pp.68-75
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• 1999

This study has observed that the dynamic behavior of Metal Matrix Composites (MMCs) in low velocity impact varies with impact velocity. MMCs with 15 fiber volume percent were fabricated by using the squeeze casting method. The AC8A was used as the matrix, and the alumina and the carbon were used as reinforcements. The tensile and vibration tests conducted yielded the yielded the tensile stress and elastic modulus of MMCs The low pass filter and instrumented impact test machine was adopted to study dynamic behaviors of MMCs corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact energy of unreinforced alloy and MM s increased as the impact velocity increased. The increase of crack propagation energy was especially prominent, but the dynamic toughness of each material did not change much. To show the relation between crack initiation energy and dynamic fracture toughness, a simple model was proposed by using the strain energy and stress distribution at notch. The model revealed that crack initiation energy is proportional to the square of dynamic fracture toughness and inversely proportional to elastic modulus.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2001.04a
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• pp.26-26
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• 2001

사무용 고지의 상당량을 차지하는 복사고지는 열과 압력으로 융착된 합성고분자 물질인 토너를 함유하고 있으며 이들 토너는 펄핑 후 크고 판상 형태의 잉크 입자를 형성하 여 기존의 부유부상법으로 제거가 곤란한 문제점을 지니고 있었다. 이러한 문제점을 극복하 는 방안으로 응집제를 이용하는 방법을 검토하였다. 복사기용 인쇄 잉크로 널리 사용되는 토너 업자는 낮은 표면에너지를 가지는 소수 성 물질이므로 같은 표면 특성을 가지는 소수성 물질과 서로 잘 결합한다. 따라서 소수성의 응집제를 이용하면 분리된 토너 잉크업자를 응집시킬 수 있으며, 응집된 토너 응집체는 스 크린 또는 클리닝 같은 정선 공정을 이용하여 제거가 가능할 것이다. 따라서 복사고지를 효 과적으로 재활용할 수 있는 탈묵방법으로 응집제를 이용하여 토너 입자를 조대한 웅집체로 형성시키고 이를 기존 탈묵방법인 스크린처리로 제거하는 방법을 검토하였다. 본 연구에서는 고급알코올의 하나언 1 -octadecanol을 이용하여 기존의 탈묵 방법 인 부유부상법으로는 제거가 곤란한 토너 잉크의 업자를 웅집시켜 구형의 조대한 응집체로 형성시켜 이를 제거하는 기술에 대하여 연구하였다. 펄핑 시의 온도를 70C의 고온으로 설 정한 경우 토너 입자가 유리전이온도에 이르게 되며 이들 토너 입자는 응집제에 의하여 웅 집되어 구형으로 성장하는 특정이 뚜렷하였으며, 토너 응집체의 크기는 최대 800 µm에 이 르기까지 조대하게 성장하였다. 또한 슬롯 폭 $250\mu\textrm{m}$의 진동 스크린 처리에 의한 토너 제 거 효율 측정 결과 역시 이들 토너 업자 웅집체의 형태가 구형임을 보여주었다. 해리 및 응 집 처 리 시 의 pH를 3으로 조정 하였을 때 토너 입 자가 웅집 제인 1 -octadecanol에 의 해 가장 효과적으로 구형의 조대한 웅집체를 이루는 것으로 나타났으며, 스크련을 통한 토너 웅집체 제거효율이 향상되었다. 복사고지 내에 포함되어 있는 전분 또는 사이즈제는 웅집 효과를 떨어뜨리는 주요 인으로 나타났다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.461-466
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• 2012

This paper describes the development and test result of X-band Transmitter flight model(FM) of STSAT-3 by satellite research center(SaTReC), KAIST. The communication sub-system of STSAT-3 is consist of two different frequency band channels. S-band frequency is used for Telemetry & Command, and X-band frequency is used for mission data. Payload observations data in Mass Memory Unit (MMU) is modulated by QPSK modulator in X-band Transmitter, and then QPSK modulation signal is transmitted to antenna through transfer switch. In this Paper, we described the results of modulation, low-pass filter design, power amp development, and switch test. The FM XTU is delivered Spacecraft Assembly, Integration and Test(AIT) level through the completion of functional Test and environmental(vibration, thermal vacuum) Test successfully.

• Applied Chemistry for Engineering
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• v.16 no.4
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• pp.588-593
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• 2005

In this study, biodegradable poly(${\varepsilon}$-caprolactone) (PCL) microcapsules containing chemically treated $SiO_2$ and nifedipine were prepared by oil-in-water (O/W) emulsion solvent evaporation method. The microcapsules containing drugs were confirmed using FT-IR spectra. The morphologies of the microcapsules were observed with scanning electron microscope (SEM). The nifedipine's release behaviors from the microcapsules were also examined with UV/vis spectroscopy. As a result, the inclusion of nifedipine into the microcapsules was determined by the presence of nifedipine's specific peak, i.e., C=O stretch vibration at $1682cm^{-1}$. The average particle size of the microcapsules decreased with increasing stirring rate. The nifedipine adsorption capacity and release rate of treated $SiO_2$ that was treated with basic solution decreased because with the increased basicity it lowered the specific surface area of $SiO_2$ and promoted stronger acid-base interactions between $SiO_2$ and nifedipine.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.300-300
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• 2014

해양환경 하에서 대형 강구조물의 경우 장기간 부식손상을 방지하기 위해 아크 용사코팅 기술이 오래전부터 유용하게 이용되어 왔다. 아크 용사코팅 기술은 타 용사코팅 기술에 비해 경제성과 생산성이 뛰어나 대형 강구조물에 적용되고 있다. 용사재료로는 Al, Zn 또는 그 합금들이 주로 사용되어 강재에 대해 희생양극 방식효과를 나타낸다. 그러나 아크용사에 의해 적층된 코팅 층은 용사공정 중 불가피하게 수많은 기공과 산화물이 포함되어 내식성 및 내구성에 악영향을 미치게 된다. 따라서 본 연구에서는 알루미늄 합금의 용사코팅 층에 대하여 다양한 후처리를 통해 내식성과 더불어 내구성을 향상시키고자 하였다. 용사코팅은 알루미늄 합금 선재(1.6 ${\varnothing}$)를 사용하여 아크용사를 실시하였다. 용사 시 용사거리는 200 mm, 공기압력은 약 $7kg/cm^2$ 정도로 유지하면서 용사코팅을 실시하여 약 $200{\mu}m$ 두께로 코팅 층을 형성시켰다. 이후 용사코팅 층의 표면에 다양한 후처리재를 적용하였으며, 내구성을 평가하기 위하여 후처리 적용 전후 시험편에 대하여 캐비테이션 실험을 실시하였다. 캐비테이션 실험은 ASTM G32-92에 의거하여 주파수 20 kHz의 초음파 진동 장치(ultrasonic vibratory device)를 사용하였다. 그리고 시험편 표면과 발진 혼에 부착된 팁(tip)과의 거리는 1 mm로 일정하게 유지시킨 뒤, 캐비테이션 발생 시간을 변수로 하여 실험을 실시하였다. 손상된 용사코팅 층의 표면은 주사전자현미경과 광학현미경으로 관찰하였으며, 시험편 손상깊이는 3D 현미경으로 비교 분석하였다. 또한 캐비테이션 실험 전후의 무게를 측정하여 무게 감소량을 상호 비교하였다. 그리고 전기화학적 실험은 천연해수 속에서 자체 제작한 홀더(holder)를 이용하여 $0.33183cm^2$의 용사코팅 층만을 노출시켜 실시하였다. 그리고 기준전극은 은/염화은 전극을, 대극은 백금전극을 사용하였다. 분극실험을 통해 후처리 적용에 따른 용사코팅 층의 부식전위 및 부식전류밀도를 비교 평가하였다. 그 결과, 용사코팅 층에 의하여 강재에 대한 희생양극 방식전위가 확보되었으며, 후처리재가 적용된 용사코팅 층에서 내식성 및 캐비테이션 저항성이 향상되었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.4
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• pp.86-93
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• 2010

The wear of railway track affects loss of rough ride, noise or vibration of train and traveling safety. Moreover as the track is worn away, this promotes destruction of structural mechanism of rail track which can bring about increasing of rail track maintenance cost drastically. For this reason, it is very important and interested research subject to design railway track structure and to analyse train movement mechanism based on systematic analysis of the reasons causing rail wear possible in real field. In this research, for the efficient maintenance, Life Cycle Performance of rail track and maintenance characteristics are computed considering some track components such as track type, contracting type, sleeper type and roadbed type. Time - Wear probabilistic distribution relationship as well as multiple regression analysis based on time, curvature and wear data are computed to predict the service life remainder of railway track and to be adapted to safety assessment.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.11
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• pp.601-611
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• 2002

As resent trends in structural construction have been to build taller and larger structures than any time in the past, they have had high flexibility and low damping that can cause large vibration response under severe environmental loading such as earthquakes, winds, and mechanical excitations. The damper with mass and sqring is one aproach to safeguarding the structure against excessive vibrations. In this paper, a large capacity hybrid-type linear motor damper(LMD) was designed and fabricated for the application to the vibration control of a large building structure model. It has been designed to be able to move the damper mass, 1,500 kg up to ${\pm}250mm$ strokes at the first mode natural frequency of the building structure model, ${\pm}0.51Hz$. Linear motor is consisted of the fixed coil and the movable NdFeB permanent magnets field part. The PM field part composed magnet modules and iron yoke, is the damper mass itself, 1500kg. LMD therefore has a simplified structure and requires a few elements in the driving system, being compared with a rotary motor damper and a hydraulic damper. However, the manufacture of large PM linear actuator is difficult because of the limit of PM size and the attraction and repulsion at the assembly of PM. Therefore, large damper system is manufactured and tested for dynamic characteristics and frequency response.