• Steel and Composite Structures
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• 제19권6호
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• pp.1549-1560
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• 2015

This paper presents the characterization of fatigue crack in the A283 Grade C steel using the MMM method by identifying the effects of magnetic flux leakage towards the crack growth rate, da/dN, and crack length. The previous and current research on the relation between MMM parameters and fatigue crack effect is still unclear and requires specific analysis to validate that. This method is considered to be a passive magnetic method among other Non-Destructive Testing (NDT) methods. The tension-tension fatigue test was conducted with a testing frequency of 10 Hz with 4 kN loaded, meanwhile the MMM response signals were captured using a MMM instrument. A correlation between the crack growth rate and magnetic flux leakage produces a sigmoid shape curve with a constant values which present the gradient, m value is in the ranges of 1.4357 to 4.0506, and the y-intercept, log C in the ranges of $4{\times}10^{-7}$ to 0.0303. Moreover, a linear relation was obtained between the crack length and magnetic flux leakage which present the R-Squared values is at 0.830 to 0.978. Therefore, MMM method has their own capability to investigate and characterize the fatigue crack effects as a main source of fracture mechanism for ferrous-based materials.

• 한국자기학회지
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• 제14권6호
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• pp.213-218
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• 2004

MBE장비를 이용하여 Mn과 Be nux의 변화를 주면서 Be-codoped GaMnAs를 성장시켰다. Mn flux의 범위는 고용체 특성의 GaMnAs에서, 과도한 nux에 의해 이차상이 형성된 상태까지 변화를 주면서 성장시켰다. Be병행 도핑 효과 연구를 위해 두 가지의 Be flux에서 박막을 성장하여 박막의 특성 변화를 관찰하였다. 과도한 Be도핑을 통해 금속성의 전도를 가지는 상태와, 상대적으로 적은 양의 도핑을 통해 캐리어의 수는 증가하였으나 반도체 전도를 보이는 상태이다. 적은 양의 Be이 병행 도핑된 GaMnAs의 경우, 상온에서 강자성 특성을 보였으나, 이차상 형성에 의한 전기 비저항의 증가와 작은 자기저항에 의해 자기 수송특성을 관찰하지 못했다. 그러나 많은 Be도핑에 의해 금속 거동을 보이는 경우에는 많은 수의 캐리어와 전기 전도토의 증가로 인해 자기 수송 특성을 관찰할 수 있었다. Be병행 도핑은 GaAs 기지 내에 효과적으로 캐리어를 공급하고, 이차상 MnAs 뿐만 아니라 MnGa의 형성을 촉진하는 것으로 생각된다.

• 대한기계학회논문집B
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• 제26권2호
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• pp.269-277
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• 2002

Experiments on the evaporation heat transfer and pressure drop in the brazed type plate heat exchangers were performed using refrigerants R410A and R22. To investigate the geometric effect, plate heat exchangers with the same pitch and height but different 45$^{\circ}$, 35$^{\circ}$and 20$^{\circ}$chevron angles are used. Tests were conducted fur the ranges of the mass flux of refrigerant from 13 kg/m$^2$s to 34 kg/m$^2$s, the evaporation temperatures of 15$^{\circ}C$, 1$0^{\circ}C$ and 5$^{\circ}C$, vapor quality from 0.15 to 0.95 and the heat flux from 2.5 kW/m$^2$to 8.5 kW/m$^2$. The evaporation heat transfer coefficients and pressure drops were measured. Most of flow patterns are in the chum flow regime and become close to the annular flow for increasing the mass flux and the vapor quality. The heat transfer coefficient increases with increasing the evaporation temperature at a given mass flux in all plate heat exchangers. Also, the pressure drop increases with increasing the mass flux and the quality and decreasing the evaporation temperature and the chevron angle.

• 한국결정성장학회지
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• 제8권4호
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• pp.532-538
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• 1998

한국산 천연베릴을 잉요하여 온도구배융제환류법에 의해 에메랄드($3BeO{\cdot}Al_2O_3{\cdot}6SiO_2:Cr^{3+}$) 단결정이 성장되었다. 리튬-몰리브데늄-바나디움 산화물계 융제는 $(MoO_3+V_2O_5)/Li_2O$, 와 $V_2O_5-Li_2O$를 서로 다르게 용융한 2종류의 융제를 혼합하여 제조하였다. 융제의 최적 조성은 산화몰리브데늄.바나디움에 대한 산화리튬의 몰비($(MoO_3+V_2O_5)/Li_2O$)가 3몰이었고 융제첨가제는 Li2O량에 대하여 $K_2O$ 또는 $Na_2O$를 0.2mole% 이내로 치환하였다. 베릴원료의 용융 농도는 융제량에 대하여 3~10% 함량이었고, $Cr_2O_3$ 발색제는 베릴량에 대하여 1%이었다. 융액은 용융, 성장, 회수 블록으로 나뉘어진 3지대 온도구배 결정성장로에서, $1100^{\circ}C$와 $1000^{\circ}C$ 사이의 안정상태에서 연속적으로 순환되도록 하였다. 에메랄드 단결정은 성장지대에서 950~$1000^{\circ}C$ 구간에서 1일 1회 2시간동안 열진동 처리하였을 때 미소핵의 생성이 억제된 대형 단결정을 성장시킬 수 있었다. 육각주상 에메랄드 단결정의 우선성장방향은 c(0001) 바닥면이었고, m(1010) 기둥면에 수직이었다.

• Korean Chemical Engineering Research
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• 제46권6호
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• pp.1075-1080
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• 2008

구연산 및 융제를 함유하는 분무용액으로부터 분무열분해법에 의해 속이 빈 전구체 분말들을 합성하고, 후열처리 과정을 거쳐 미세 $Gd_2O_3:Eu$ 형광체를 합성하였다. 구연산은 전구체 분말들의 다공성을 증대시킴으로써 후열처리 후에 미세 형광체 합성이 가능하게 하였다. 구연산을 첨가하지 않은 분무용액으로부터 합성된 형광체는 수 마이크론 크기를 가졌다. 융제는 형광체 분말의 크기와 자외선 하에서의 발광세기를 증대시켰다. 여러 가지 용제 중 휘도가 우수한 초미세 $Gd_2O_3:Eu$ 형광체 합성에는 $Li_2CO_3$가 적절하였다. $Li_2CO_3$ 융제의 첨가량이 형광체의 3 wt% 이하일 때 소성 온도 $1,050^{\circ}C$ 및 $1,050^{\circ}C$에서 합성된 형광체들은 서브마이크론 크기를 가졌다. 소성 온도 $1,050^{\circ}C$에서 얻어진 형광체의 발광 세기는 소성온도 $1,050^{\circ}C$에서 얻어진 형광체의 124%였다.

• 천문학회보
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• 제40권1호
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• pp.64.3-64.3
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• 2015

We have developed a set of daily solar flare peak flux forecast models for strong flares using multiple linear regression and artificial neural network methods. We consider input parameters as solar activity data from January 1996 to December 2013 such as sunspot area, X-ray flare peak flux and weighted total flux of previous day, and mean flare rates of McIntosh sunspot group (Zpc) and Mount Wilson magnetic classification. For a training data set, we use the same number of 61 events for each C-, M-, and X-class from Jan. 1996 to Dec. 2004, while other previous models use all flares. For a testing data set, we use all flares from Jan. 2005 to Nov. 2013. The best three parameters related to the observed flare peak flux are weighted total flare flux of previous day (r = 0.51), X-ray flare peak flux (r = 0.48), and Mount Wilson magnetic classification (r = 0.47). A comparison between our neural network models and the previous models based on Heidke Skill Score (HSS) shows that our model for X-class flare is much better than the models and that for M-class flares is similar to them. Since all input parameters for our models are easily available, the models can be operated steadily and automatically in near-real time for space weather service.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.519-521
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• 1996

Emerald (3BeO.Al2O3.6SiO2 : Cr3+) single crystals were crystals were grown by reflux method of temperature gradient in the flux solution of Li2O-MoO3-V2O5 system. The composition of flux materials were 3 mole ratio of MoO3-V2O5/Li2O, subtituted 0.2 mole% of K2O, Na2O, Nb2O5 etc to Li2O content, solved 10-15% of beryl to flux quantity and doped 1% of Cr2O3 to emerald amount. Those of mixing were melted at 110$0^{\circ}C$ in Pt containers of the 3 zone furnace of melt-growth-return to circulate continniously, specially it has been grown large emerald single crystal when thermal fluctuation was treated for 2hrs of once time a day at 1050-95$0^{\circ}C$ in growth zone, substitutional solid solution effect of Cr+3 ion for Al+3 to the growth of emerald single crystal was good. Emerald single crystals were c(0001) hexagonal crystal face of preferencial growth direction and m(1010) post side. When it had been durated for 5 months emerald single crystals of the firet size of 0.6mm thickness of seed crystal were grown 32$\times$65mm(c x m) of maximum size and 6.2mm thickness.

• 천문학회보
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• 제44권1호
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• pp.35.3-35.3
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• 2019

Blazars are a subclass of active galactic nuclei (AGNs) with relativistic jets aligned with our line of sight. The jet physics is yet to be understood, but can be studied with blazar variability (e.g., flares). The highly variable blazar 3C 279 has shown a general decline of its radio flux density since 2013, but the flux density has been increasing since 2017. To better understand physical properties of 3C 279 related with the flux variations, we analyze multi-frequency new radio data obtained with Korean VLBI Network (KVN), as well as archival data from Owens Valley Radio Observatory (OVRO) and Submillimeter Array (SMA). We measure the radio spectral variability and infer the relativistic jet properties of 3C 279. The high-cadence OVRO and SMA observations are used to construct detailed light curves of the source, and KVN data supplement the spectral coverage and allow us to locate the spectral break frequencies precisely. In this talk, we present our analysis results and interpret them using a blazar jet model.

• 한국정밀공학회지
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• 제9권2호
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• pp.52-60
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• 1992

In this study on the development of the heat flux sensor, unlike the common heat-flux sensor with thermocouple, the heat-treated adhesive-tupe film nickel-gauge was used in measuring temperature. The proposed its Ni-gauge is bound to be compatible with platinum gauge(Pt-Gauge) in its linearity. It is also considered to be cheap in economical sense. In the evaluation of it's performance, the numerical analysis is essential to investigate charateristics of proper sensor and the adequate analsis is depended upon boundary conditions and actual conditions. There are many types of heat flux sensor in the market, and adhexive type flux sensor is most common. In the present investigation, this type of heat flux sensor had been chosen. The figure of the sensor under consideration is an open cavity type, which is calculated numerically by SIMPLER algorithm. The temperature distributions of the sensor predicted by numerical calculation for steady and unsteady states are able to give the chacteristics of the adhesive type heat flux sensor(1st heat flux sensor) according to the heat flux. It means that the outvoltage, the sensitivity, and the performances of responsibility could be evaluated as a result. Through this analysis improved heat flux sensor(2nd heat flux sensor) could be predicted with the reflection of proper operating temperature($150^{\circ}C$) of the Ni-gauge.

• 한국해양환경ㆍ에너지학회지
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• 제17권1호
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• pp.13-19
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• 2014

막분리법에 의한 해수 담수화시 공급 원수 온도는 막성능에 영향을 미친다. 특히 폐열원을 이용하여 분리막 투과량을 증대시키고자 하는 경우에는 고온의 공급 원수가 분리막 성능에 미치는 영향을 정확히 분석하여 적용하는 것이 필요하다. 온도에 의한 막투과 성능 분석을 위해 $10^{\circ}C$에서 $60^{\circ}C$까지 공급 해수 온도를 변화시키면서 실험을 실시하였다. 온도가 상승하면서 투과량이 증가하는 경향을 물의 점성 변화와 막의 변화로 나누어서 분석하였다. NF 막에서는 온도에 따른 물의 점성 변화로 투과량 변화를 예측할 수 있었으나 RO막의 경우는 물의 점성변화로 예측한 투과량과 실험에 의한 투과량은 $60^{\circ}C$에서 30%정도 차이가 나타났다. 이는 RO막이 원수 온도가 상승함에 따라 막의 수축이 일어나 공극의 크기가 8%정도 감소함에 기인하는 것으로 추정된다. 따라서 막분리식 해수 담수화에서 투과량을 증대시키기 위한 온도 상승은 막변형이 일어나지 않는 범위 내에서 효과적으로 수행하여야 할 것이다.