• 한국세라믹학회지
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• 제27권5호
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• pp.684-692
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• 1990

Ultrafine magnetite powder for the ferromagnetic fluid was prepared by an addition of alkaline solution to the solution containing Fe2+ and Fe3+ ions at 6$0^{\circ}C$. The optimum condition of the magnetite synthesis was delineated by examining such various physico-chemical properties as Fe2+/Fe+3 ratio in the powder, phase characteristics, MHC and $\sigma$max. A new scheme for the steric stabilization of colloidal dispersion was proposed using the concept of the buffer group action for the increased interfacial density of the stabilizing moieties at colloid particle/dispersion medium interface. The proposed concept was successfully applied to the preparation of the kinetically stable kerosinebased ferrofluid using Tween and Span as dispersants. In the dispersion of magnetite particles in a kerosine, Tween(polyoxyethylene sorbitan oleate) acts as a primary stabilizer which provides an anchor group, whereas Span(sorbitan oleate) can be classified as a secondary stabilizer which adsorbs on the surface of magnetite particle through the action of the buffer group. Dispersion studies using various quantities of Tween and Span supported the concept of the buffer group action for increased dispersion characteristics of the kerosine based ferromagnetic fluid.

• Wind and Structures
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• 제9권1호
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• pp.59-74
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• 2006

Vertical stabilizer plates have been found to be an effective aerodynamic measure to improve the aerodynamic stability of bridges either with an open cross section or with a streamlined box cross section in wind tunnel testings and have been adopted in some long span bridges. By taking an open deck II-shaped section and a closed box section as examples, the mechanism of vertical stabilizer plates for improving aerodynamic stability are investigated by using numerical simulation based on Random Vortex Method. It is found that vertical stabilizer plates can increase the amplitude of the heaving motion, and decrease that of the rotational motion of the bridge decks.

• Wind and Structures
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• 제12권3호
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• pp.205-217
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• 2009

Aerodynamic flutter control for long-span cable-supported bridges was investigated based on three basic girder sections, i.e. streamlined box girder section, box girder section with cantilevered slabs and two-isolated-girder section. Totally four kinds of aerodynamic flutter control measures (adding fairings, central-slotting, adding central stabilizers and adjusting the position of inspection rail) were included in this research. Their flutter control effects on different basic girder sections were evaluated by sectional model or aeroelastic model wind tunnel tests. It is found that all basic girder sections can get aerodynamically more stabled with appropriate aerodynamic flutter control measures, while the control effects are influenced by the details of control measures and girder section configurations. The control effects of the combinations of these four kinds of aerodynamic flutter control measures, such as central-slotting plus central-stabilizer, were also investigated through sectional model wind tunnel tests, summarized and compared to the flutter control effect of single measure respectively.

• 폴리머
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• 제25권4호
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• pp.460-467
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• 2001

Sorbitan ester(Span)와 2,2'-azobis(2-methyl propionamidine) dihydrochloride(AIBA)를 각각 입자안정제와 개시제로 사용하여 cyclohexane 분산매에서 acrylamide (AM)의 역상 현탁중합을 다양한 중합 조건하에서 수행하여 생성되는 poly(acrylamide)(PAM) 현탁입자의 입자경, 평균분자량, 수용화도 등을 조사하였다. 일반적으로 PAM 현탁입자경은 입자안정제의 농도, 진탕속도, 수용상 성분 중 물의 양이 증가함에 따라, 또는 개시제의 농도, 중합 온도가 감소함에 따라 감소하였다. PAM 현탁중합체의 평균분자량은 단량체의 농도, 입자안정제의 농도가 증가함에 따라, 또는 개시제의 농도, 중합 온도, 수용상 성분중 물의 농도가 감소함에 따라 증가하였다. 본 연구에서 얻어진 PAM 현탁입자는 구슬형의 약 2 ~ 50 ${\mu}$m 범위의 입자경과 약 800 ~ 1200만의 중량평균분자량을 나타내었다.

• 정보저장시스템학회논문집
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• 제7권1호
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• pp.25-30
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• 2011

In the last couple of years, the flexible optical disk(FOD) system that consists of a thin polycarbonate(PC) film of 95 ${\mu}m$ thick, a rigid stabilizer, and a high speed spindle motor has been spot-lighted as the next-generation optical system for archival use of digital data. The air film between the rotating disk and stabilizer provides a means for damping out the lateral disk vibrations. However, its damping-capability drops significantly as the rotational speed of the disk exceeds a specific limit and, eventually, the disk vibration propagates inward causing the whole span of the disk exhibits large vibration amplitudes. Based on the numerical simulations as well as the experimental results, the present work aims to evaluate the damping coefficient of the air-film near the outer region of the disk where the capillary type orifices are applied to the edge of the curved stabilizer.

• Wind and Structures
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• 제12권4호
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• pp.285-298
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• 2009

For long-span suspension bridges with their intrinsic limit in flutter, some counter measures, for example, central stabilizers, should be adopted to improve aerodynamic stability to meet with the appropriate wind resistance requirements. The present paper introduces aerodynamic stabilization for long-span suspension bridges with box girders by using central stabilizers based on Xihoumen Bridge with the main span of 1650 m. The aerodynamic stabilization study covers experimental investigation of sectional model testing, comprehensive evaluation of three central stabilizers and theoretical analysis of stabilizing mechanism related to flutter derivatives, aerodynamic damping and degree participation.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2008년도 추계학술대회 논문집
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• pp.7-11
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• 2008

형광등은 방전등의 일종으로 방전현상을 이용하여 전기에너지를 빛으로 변환하는 광원으로 램프의 점등 시에 나타나는 부저항 특성 때문에 반드시 점등회로를 필요로 한다. 방전등의 광원특성과 안정기의 변환특성은 밀접한 관련을 가지고 있다. 따라서 양 특성의 정합성립을 위하여 사용조건 및 경제성을 고려한 최적회로 설계지침을 내놓는 것은 매우 중요하다. 본 논문에서는 형광등용 전자안정기에 있어 부하인 형광램프의 수명말기에 나타나는 화재, 광효율 저감 등 여러 가지 문제점을 개선할 수 있는 수명말기 검측과 수명말기 표시기능 개발에 대하여 고찰해본다.

• Wind and Structures
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• 제32권5호
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• pp.423-437
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• 2021

Aerodynamic measures have been widely used for improving the flutter stability of long-span bridges, and this paper focuses their windproof ability to improve the wind environment for vehicles. The whole wind environment around a long-span bridge located in high altitude mountainous areas is first studied. The local wind environment above the deck is then focused by two perspectives. One is the windproof effects of aerodynamic measures, and the other is whether the bridge with aerodynamic measures meets the requirement of flutter stability after installing extra wind barriers in the future. Furthermore, the effects of different wind barriers are analyzed. Results show that aerodynamic measures exert potential effects on the local wind environment, as the vertical stabilizer obviously reduces wind velocities behind it while the closed central slot has limited effects. The suggested aerodynamic measures have the ability to offset the adverse effect of the wind barrier on the flutter stability of the bridge. Behind the wind barrier, wind velocities decrease in general, but in some places incoming flow has to pass through the deck with higher velocities due to the increase in blockage ratio. Further comparison shows that the wind barrier with four bars is optimal.

• 한국응용과학기술학회지
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• 제31권1호
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• pp.92-100
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• 2014

비이온계면활성제 가운데 솔비톨계 계면활성제인 Span을 이용해 수열합성법으로 수산화마그네슘을 합성하였다. 수산화마그네슘 합성의 전구체는 염화마그네슘과 수산화나트륨을 사용하였다. 비이온 계면활성제는 안정제와 분산제 그리고 표면 개질제로 적용하였다. 비이온 계면활성제를 첨가하였을 경우 수산화마그네슘 입자는 좀 더 작고 균일한 크기와 좋은 분산성을 나타내었으며, 소수성 성질을 나타내었다. 합성된 입자의 특성은 PSA, SEM, EDS, XRD 그리고 FT-IR을 통해 확인하였다. 기기 분석을 통해 개질 전과 후의 수산화마그네슘의 소수성, 분산성 특성을 비교하였다. 또한 실험조건에 따라 수산화마그네슘 입자의 표면 개질 특성 변화를 확인하였다.

• Journal of Magnetics
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• 제20권4호
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• pp.371-376
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• 2015

Magnetite nanoparticles were synthesized by adding excess ammonium hydroxide to a solution of iron (II) and (III) chlorides. The surfactants of oleic acid and Span 80 were applied in sequence to the magnetic particles as a combined stabilizer, and poly-${\alpha}$-olefin (PAO) 30 or 60 was used as the liquid base with a low or high viscosity, respectively. The ferrofluids were prepared with the concentrations of 200, 300, 400, and 500 mg/mL, and characterized by density, dispersion, magnetization, and viscosity. The density of the fluids increased proportionally to the concentration from 0.98 to 1.27 g/mL and 1.01 to 1.30 g/mL with PAO 30 base and PAO 60 base, and the dispersion stability was 77-95 and 81-74% for the PAO-30 and PAO-60-based fluids, respectively. The observed saturation magnetization values of the PAO-30 and PAO-60-based ferrofluids were 16 to 42 mT and 17 to 41 mT with the concentration increase in the range 200-500 mg/mL, respectively, depending upon the content of magnetic particles in the fluid. The viscosity variation of the PAO-30 and PAO-60-based ferrofluids in the temperature range $20-80^{\circ}C$ was the least with the concentrations of 400 and 300 mg/mL, respectively.